This is zsh.info, produced by makeinfo version 4.8 from tzsh.texi.

INFO-DIR-SECTION Utilities
START-INFO-DIR-ENTRY
* ZSH: (zsh).                     The Z Shell Manual.
END-INFO-DIR-ENTRY


File: zsh.info,  Node: Top,  Next: The Z Shell Manual,  Prev: (dir),  Up: (dir)

The Z Shell Manual
******************

   This Info file documents Zsh, a freely available UNIX command
interpreter (shell), which of the standard shells most closely
resembles the Korn shell (ksh), although it is not completely
compatible.  Zsh is able to emulate POSIX shells, but its default mode
is not POSIX compatible, either.

Version 5.9.1, last updated May 31, 2026.

* Menu:

* The Z Shell Manual::
* Introduction::
* Roadmap::
* Invocation::
* Files::
* Shell Grammar::
* Redirection::
* Command Execution::
* Functions::
* Jobs & Signals::
* Arithmetic Evaluation::
* Conditional Expressions::
* Prompt Expansion::
* Expansion::
* Parameters::
* Options::
* Shell Builtin Commands::
* Zsh Line Editor::
* Completion Widgets::
* Completion System::
* Completion Using compctl::
* Zsh Modules::
* Calendar Function System::
* TCP Function System::
* Zftp Function System::
* User Contributions::

--- Indices ---

* Concept Index::
* Variables Index::
* Options Index::
* Functions Index::
* Editor Functions Index::
* Style and Tag Index::

 --- The Detailed Node Listing ---

Introduction

* Author::
* Availability::
* Mailing Lists::
* The Zsh FAQ::
* The Zsh Web Page::
* The Zsh Userguide::
* See Also::

Invocation

* Compatibility::
* Restricted Shell::

Shell Grammar

* Simple Commands & Pipelines::
* Precommand Modifiers::
* Complex Commands::
* Alternate Forms For Complex Commands::
* Reserved Words::
* Comments::
* Aliasing::
* Quoting::

Expansion

* History Expansion::
* Process Substitution::
* Parameter Expansion::
* Command Substitution::
* Arithmetic Expansion::
* Brace Expansion::
* Filename Expansion::
* Filename Generation::

Parameters

* Array Parameters::
* Positional Parameters::
* Local Parameters::
* Parameters Set By The Shell::
* Parameters Used By The Shell::

Options

* Specifying Options::
* Description of Options::
* Option Aliases::
* Single Letter Options::

Zsh Line Editor

* Keymaps::
* Zle Builtins::
* Zle Widgets::
* User-Defined Widgets::
* Standard Widgets::
* Character Highlighting::

Completion Widgets

* Completion Special Parameters::
* Completion Builtin Commands::
* Completion Condition Codes::
* Completion Matching Control::
* Completion Widget Example::

Completion System

* Initialization::
* Completion System Configuration::
* Control Functions::
* Bindable Commands::
* Completion Functions::
* Completion Directories::

Completion Using compctl

* Command Flags::
* Option Flags::
* Alternative Completion::
* Extended Completion::
* Example::

Zsh Modules

* The zsh/attr Module::
* The zsh/cap Module::
* The zsh/clone Module::
* The zsh/compctl Module::
* The zsh/complete Module::
* The zsh/complist Module::
* The zsh/computil Module::
* The zsh/curses Module::
* The zsh/datetime Module::
* The zsh/db/gdbm Module::
* The zsh/deltochar Module::
* The zsh/example Module::
* The zsh/files Module::
* The zsh/langinfo Module::
* The zsh/mapfile Module::
* The zsh/mathfunc Module::
* The zsh/nearcolor Module::
* The zsh/newuser Module::
* The zsh/parameter Module::
* The zsh/pcre Module::
* The zsh/param/private Module::
* The zsh/regex Module::
* The zsh/sched Module::
* The zsh/net/socket Module::
* The zsh/stat Module::
* The zsh/system Module::
* The zsh/net/tcp Module::
* The zsh/termcap Module::
* The zsh/terminfo Module::
* The zsh/watch Module::
* The zsh/zftp Module::
* The zsh/zle Module::
* The zsh/zleparameter Module::
* The zsh/zprof Module::
* The zsh/zpty Module::
* The zsh/zselect Module::
* The zsh/zutil Module::

Calendar Function System

* Calendar File and Date Formats::
* Calendar System User Functions::
* Calendar Styles::
* Calendar Utility Functions::
* Calendar Bugs::

TCP Function System

* TCP Functions::
* TCP Parameters::
* TCP Examples::
* TCP Bugs::

Zftp Function System

* Installation::
* Zftp Functions::
* Miscellaneous Features::

User Contributions

* Utilities::
* Recent Directories::
* Other Directory Functions::
* Version Control Information::
* Prompt Themes::
* ZLE Functions::
* Exception Handling::
* MIME Functions::
* Mathematical Functions::
* User Configuration Functions::
* Other Functions::


File: zsh.info,  Node: The Z Shell Manual,  Next: Introduction,  Prev: Top,  Up: Top

1 The Z Shell Manual
********************

This document has been produced from the texinfo file zsh.texi,
included in the Doc sub-directory of the Zsh distribution.

1.1 Producing documentation from zsh.texi
=========================================

The texinfo source may be converted into several formats:


The Info manual
     The Info format allows searching for topics, commands, functions,
     etc.  from the many Indices. The command `makeinfo zsh.texi' is
     used to produce the Info documentation.

The printed manual
     The command `texi2dvi zsh.texi' will output zsh.dvi which can then
     be processed with `dvips' and optionally `gs' (Ghostscript) to
     produce a nicely formatted printed manual.

The HTML manual
     An HTML version of this manual is available at the Zsh web site
     via:

     `https://zsh.sourceforge.io/Doc/'.

     (The HTML version is produced with `texi2html', which may be
     obtained from `http://www.nongnu.org/texi2html/'. The command is
     `texi2html -output .  -ifinfo -split=chapter -node-files zsh.texi'.
     If necessary, upgrade to version 1.78 of texi2html.)


For those who do not have the necessary tools to process texinfo,
precompiled documentation (PostScript, dvi, PDF, info and HTML formats)
is available from the zsh archive site or its mirrors, in the file
zsh-doc.tar.gz. (See *Note Availability:: for a list of sites.)


File: zsh.info,  Node: Introduction,  Next: Roadmap,  Prev: The Z Shell Manual,  Up: Top

2 Introduction
**************

Zsh is a UNIX command interpreter (shell) usable as an interactive
login shell and as a shell script command processor.  Of the standard
shells, zsh most closely resembles `ksh' but includes many
enhancements.  It does not provide compatibility with POSIX or other
shells in its default operating mode:  see the section *Note
Compatibility::.

Zsh has command line editing, builtin spelling correction, programmable
command completion, shell functions (with autoloading), a history
mechanism, and a host of other features.

* Menu:

* Author::
* Availability::
* Mailing Lists::
* The Zsh FAQ::
* The Zsh Web Page::
* The Zsh Userguide::
* See Also::


File: zsh.info,  Node: Author,  Next: Availability,  Up: Introduction

2.1 Author
==========

Zsh was originally written by Paul Falstad.  Zsh is now maintained by
the members of the zsh-workers mailing list <zsh-workers@zsh.org>.  The
development is currently coordinated by Peter Stephenson <pws@zsh.org>.
The coordinator can be contacted at <coordinator@zsh.org>, but matters
relating to the code should generally go to the mailing list.


File: zsh.info,  Node: Availability,  Next: Mailing Lists,  Prev: Author,  Up: Introduction

2.2 Availability
================

Zsh is available from the following HTTP and anonymous FTP site.

`ftp://ftp.zsh.org/pub/'
`https://www.zsh.org/pub/'

The up-to-date source code is available via Git from Sourceforge.  See
`https://sourceforge.net/projects/zsh/' for details.  A summary of
instructions for the archive can be found at
`https://zsh.sourceforge.io/'.




File: zsh.info,  Node: Mailing Lists,  Next: The Zsh FAQ,  Prev: Availability,  Up: Introduction

2.3 Mailing Lists
=================

Zsh has several mailing lists:


<zsh-announce@zsh.org>
     Announcements about releases, major changes in the shell and the
     monthly posting of the Zsh FAQ.  (moderated)

<zsh-users@zsh.org>
     User discussions.

<zsh-workers@zsh.org>
     Hacking, development, bug reports and patches.

<zsh-security@zsh.org>
     Private mailing list (the general public cannot subscribe to it)
     for discussing bug reports with security implications, i.e.,
     potential vulnerabilities.

     If you find a security problem in zsh itself, please mail this
     address.


To subscribe or unsubscribe, send mail to the associated administrative
address for the mailing list.


<zsh-announce-subscribe@zsh.org>

<zsh-users-subscribe@zsh.org>

<zsh-workers-subscribe@zsh.org>


<zsh-announce-unsubscribe@zsh.org>

<zsh-users-unsubscribe@zsh.org>

<zsh-workers-unsubscribe@zsh.org>


YOU ONLY NEED TO JOIN ONE OF THE MAILING LISTS AS THEY ARE NESTED.  All
submissions to `zsh-announce' are automatically forwarded to
`zsh-users'.  All submissions to `zsh-users' are automatically
forwarded to `zsh-workers'.

If you have problems subscribing/unsubscribing to any of the mailing
lists, send mail to <listmaster@zsh.org>.

The mailing lists are archived; the archives can be accessed via the
administrative addresses listed above.  There is also a hypertext
archive available at `https://www.zsh.org/mla/'.


File: zsh.info,  Node: The Zsh FAQ,  Next: The Zsh Web Page,  Prev: Mailing Lists,  Up: Introduction

2.4 The Zsh FAQ
===============

Zsh has a list of Frequently Asked Questions (FAQ), maintained by Peter
Stephenson <pws@zsh.org>.  It is regularly posted to the newsgroup
`comp.unix.shell' and the `zsh-announce' mailing list.  The latest
version can be found at any of the Zsh FTP sites, or at
`https://www.zsh.org/FAQ/'.  The contact address for FAQ-related matters
is <faqmaster@zsh.org>.


File: zsh.info,  Node: The Zsh Web Page,  Next: The Zsh Userguide,  Prev: The Zsh FAQ,  Up: Introduction

2.5 The Zsh Web Page
====================

Zsh has a web page which is located at `https://www.zsh.org/'.  The
contact address for web-related matters is <webmaster@zsh.org>.


File: zsh.info,  Node: The Zsh Userguide,  Next: See Also,  Prev: The Zsh Web Page,  Up: Introduction

2.6 The Zsh Userguide
=====================

A userguide is currently in preparation.  It is intended to complement
the manual, with explanations and hints on issues where the manual can
be cabbalistic, hierographic, or downright mystifying (for example, the
word `hierographic' does not exist).  It can be viewed in its current
state at `https://zsh.sourceforge.io/Guide/'.  At the time of writing,
chapters dealing with startup files and their contents and the new
completion system were essentially complete.


File: zsh.info,  Node: See Also,  Prev: The Zsh Userguide,  Up: Introduction

2.7 See Also
============

sh(1), csh(1), tcsh(1), rc(1), bash(1), ksh(1)

`IEEE Standard for information Technology - Portable Operating System
Interface (POSIX) - Part 2: Shell and Utilities', IEEE Inc, 1993, ISBN
1-55937-255-9.


File: zsh.info,  Node: Roadmap,  Next: Invocation,  Prev: Introduction,  Up: Top

3 Roadmap
*********

The Zsh Manual, like the shell itself, is large and often complicated.
This section of the manual provides some pointers to areas of the shell
that are likely to be of particular interest to new users, and indicates
where in the rest of the manual the documentation is to be found.



3.1 When the shell starts
=========================

When it starts, the shell reads commands from various files.  These can
be created or edited to customize the shell.  See *Note Files::.

If no personal initialization files exist for the current user, a
function is run to help you change some of the most common settings.
It won't appear if your administrator has disabled the zsh/newuser
module.  The function is designed to be self-explanatory.  You can run
it by hand with `autoload -Uz zsh-newuser-install; zsh-newuser-install
-f'.  See also *Note User Configuration Functions::.



3.2 Interactive Use
===================

Interaction with the shell uses the builtin Zsh Line Editor, ZLE.  This
is described in detail in *Note Zsh Line Editor::.

The first decision a user must make is whether to use the Emacs or Vi
editing mode as the keys for editing are substantially different.  Emacs
editing mode is probably more natural for beginners and can be selected
explicitly with the command bindkey -e.

A history mechanism for retrieving previously typed lines (most simply
with the Up or Down arrow keys) is available; note that, unlike other
shells, zsh will not save these lines when the shell exits unless you
set appropriate variables, and the number of history lines retained by
default is quite small (30 lines).  See the description of the shell
variables (referred to in the documentation as parameters) HISTFILE,
HISTSIZE and SAVEHIST in *Note Parameters Used By The Shell::.  Note
that it's currently only possible to read and write files saving history
when the shell is interactive, i.e. it does not work from scripts.

The shell now supports the UTF-8 character set (and also others if
supported by the operating system).  This is (mostly) handled
transparently by the shell, but the degree of support in terminal
emulators is variable.  There is some discussion of this in the shell
FAQ, `https://www.zsh.org/FAQ/'.  Note in particular that for combining
characters to be handled the option COMBINING_CHARS needs to be set.
Because the shell is now more sensitive to the definition of the
character set, note that if you are upgrading from an older version of
the shell you should ensure that the appropriate variable, either LANG
(to affect all aspects of the shell's operation) or LC_CTYPE (to affect
only the handling of character sets) is set to an appropriate value.
This is true even if you are using a single-byte character set
including extensions of ASCII such as ISO-8859-1 or ISO-8859-15.  See
the description of LC_CTYPE in *Note Parameters::.



3.2.1 Completion
----------------

Completion is a feature present in many shells. It allows the user to
type only a part (usually the prefix) of a word and have the shell fill
in the rest.  The completion system in zsh is programmable.  For
example, the shell can be set to complete email addresses in arguments
to the mail command from your ~/.abook/addressbook; usernames,
hostnames, and even remote paths in arguments to scp, and so on.
Anything that can be written in or glued together with zsh can be the
source of what the line editor offers as possible completions.

Zsh has two completion systems, an old, so called compctl completion
(named after the builtin command that serves as its complete and only
user interface), and a new one, referred to as compsys, organized as
library of builtin and user-defined functions.  The two systems differ
in their interface for specifying the completion behavior.  The new
system is more customizable and is supplied with completions for many
commonly used commands; it is therefore to be preferred.

The completion system must be enabled explicitly when the shell starts.
For more information see *Note Completion System::.



3.2.2 Extending the line editor
-------------------------------

Apart from completion, the line editor is highly extensible by means of
shell functions.  Some useful functions are provided with the shell;
they provide facilities such as:


insert-composed-char
     composing characters not found on the keyboard

match-words-by-style
     configuring what the line editor considers a word when moving or
     deleting by word

history-beginning-search-backward-end, etc.
     alternative ways of searching the shell history

replace-string, replace-pattern
     functions for replacing strings or patterns globally in the
     command line

edit-command-line
     edit the command line with an external editor.


See *Note ZLE Functions:: for descriptions of these.



3.3 Options
===========

The shell has a large number of options for changing its behaviour.
These cover all aspects of the shell; browsing the full documentation is
the only good way to become acquainted with the many possibilities.  See
*Note Options::.



3.4 Pattern Matching
====================

The shell has a rich set of patterns which are available for file
matching (described in the documentation as `filename generation' and
also known for historical reasons as `globbing') and for use when
programming.  These are described in *Note Filename Generation::.

Of particular interest are the following patterns that are not commonly
supported by other systems of pattern matching:


**
     for matching over multiple directories

|
     for matching either of two alternatives

~, ^
     the ability to exclude patterns from matching when the
     EXTENDED_GLOB option is set

(...)
     glob qualifiers, included in parentheses at the end of the pattern,
     which select files by type (such as directories) or attribute
     (such as size).



3.5 General Comments on Syntax
==============================

Although the syntax of zsh is in ways similar to the Korn shell, and
therefore more remotely to the original UNIX shell, the Bourne shell,
its default behaviour does not entirely correspond to those shells.
General shell syntax is introduced in *Note Shell Grammar::.

One commonly encountered difference is that variables substituted onto
the command line are not split into words.  See the description of the
shell option SH_WORD_SPLIT in *Note Parameter Expansion::.  In zsh, you
can either explicitly request the splitting (e.g. ${=foo}) or use an
array when you want a variable to expand to more than one word.  See
*Note Array Parameters::.



3.6 Programming
===============

The most convenient way of adding enhancements to the shell is typically
by writing a shell function and arranging for it to be autoloaded.
Functions are described in *Note Functions::.  Users changing from the
C shell and its relatives should notice that aliases are less used in
zsh as they don't perform argument substitution, only simple text
replacement.

A few general functions, other than those for the line editor described
above, are provided with the shell and are described in *Note User
Contributions::.  Features include:


promptinit
     a prompt theme system for changing prompts easily, see *Note
     Prompt Themes::

zsh-mime-setup
     a MIME-handling system which dispatches commands according to the
     suffix of a file as done by graphical file managers

zcalc
     a calculator

zargs
     a version of xargs that makes the find command redundant

zmv
     a command for renaming files by means of shell patterns.



File: zsh.info,  Node: Invocation,  Next: Files,  Prev: Roadmap,  Up: Top

4 Invocation
************



4.1 Invocation
==============

The following flags are interpreted by the shell when invoked to
determine where the shell will read commands from:


-c
     Take the first argument as a command to execute, rather than
     reading commands from a script or standard input.  If any further
     arguments are given, the first one is assigned to $0, rather than
     being used as a positional parameter.

-i
     Force shell to be interactive.  It is still possible to specify a
     script to execute.

-s
     Force shell to read commands from the standard input.  If the -s
     flag is not present and an argument is given, the first argument
     is taken to be the pathname of a script to execute.


If there are any remaining arguments after option processing, and
neither of the options -c or -s was supplied, the first argument is
taken as the file name of a script containing shell commands to be
executed.  If the option PATH_SCRIPT is set, and the file name does not
contain a directory path (i.e. there is no `/' in the name), first the
current directory and then the command path given by the variable PATH
are searched for the script.  If the option is not set or the file name
contains a `/' it is used directly.

After the first one or two arguments have been appropriated as
described above, the remaining arguments are assigned to the positional
parameters.

For further options, which are common to invocation and the set
builtin, see *Note Options::.

The long option `--emulate' followed (in a separate word) by an
emulation mode may be passed to the shell.  The emulation modes are
those described for the emulate builtin, see *Note Shell Builtin
Commands::.  The `--emulate' option must precede any other options
(which might otherwise be overridden), but following options are
honoured, so may be used to modify the requested emulation mode.  Note
that certain extra steps are taken to ensure a smooth emulation when
this option is used compared with the emulate command within the shell:
for example, variables that conflict with POSIX usage such as path are
not defined within the shell.

Options may be specified by name using the -o option.  -o acts like a
single-letter option, but takes a following string as the option name.
For example,


     zsh -x -o shwordsplit scr

runs the script scr, setting the XTRACE option by the corresponding
letter `-x' and the SH_WORD_SPLIT option by name.  Options may be
turned _off_ by name by using +o instead of -o.  -o can be stacked up
with preceding single-letter options, so for example `-xo shwordsplit'
or `-xoshwordsplit' is equivalent to `-x -o shwordsplit'.

Options may also be specified by name in GNU long option style,
`--OPTION-NAME'.  When this is done, `-' characters in the option name
are permitted: they are translated into `_', and thus ignored.  So, for
example, `zsh --sh-word-split' invokes zsh with the SH_WORD_SPLIT
option turned on.  Like other option syntaxes, options can be turned
off by replacing the initial `-' with a `+'; thus `+-sh-word-split' is
equivalent to `--no-sh-word-split'.  Unlike other option syntaxes,
GNU-style long options cannot be stacked with any other options, so for
example `-x-shwordsplit' is an error, rather than being treated like
`-x --shwordsplit'.

The special GNU-style option `--version' is handled; it sends to
standard output the shell's version information, then exits
successfully.  `--help' is also handled; it sends to standard output a
list of options that can be used when invoking the shell, then exits
successfully.

Option processing may be finished, allowing following arguments that
start with `-' or `+' to be treated as normal arguments, in two ways.
Firstly, a lone `-' (or `+') as an argument by itself ends option
processing.  Secondly, a special option `--' (or `+-'), which may be
specified on its own (which is the standard POSIX usage) or may be
stacked with preceding options (so `-x-' is equivalent to `-x --').
Options are not permitted to be stacked after `--' (so `-x-f' is an
error), but note the GNU-style option form discussed above, where
`--shwordsplit' is permitted and does not end option processing.

Except when the `sh'/`ksh' emulation single-letter options are in
effect, the option `-b' (or `+b') ends option processing.  `-b' is like
`--', except that further single-letter options can be stacked after
the `-b' and will take effect as normal.



* Menu:

* Compatibility::
* Restricted Shell::



File: zsh.info,  Node: Compatibility,  Next: Restricted Shell,  Up: Invocation

4.2 Compatibility
=================

Zsh tries to emulate `sh' or `ksh' when it is invoked as sh or ksh
respectively; more precisely, it looks at the first letter of the name
by which it was invoked, excluding any initial `r' (assumed to stand
for `restricted'), and if that is `b', `s' or `k' it will emulate `sh'
or `ksh'.  Furthermore, if invoked as su (which happens on certain
systems when the shell is executed by the su command), the shell will
try to find an alternative name from the SHELL environment variable and
perform emulation based on that.

In `sh' and `ksh' compatibility modes the following parameters are not
special and not initialized by the shell: ARGC, argv, cdpath, fignore,
fpath, HISTCHARS, mailpath, MANPATH, manpath, path, prompt, PROMPT,
PROMPT2, PROMPT3, PROMPT4, psvar, status.

The usual zsh startup/shutdown scripts are not executed.  Login shells
source /etc/profile followed by $HOME/.profile.  If the ENV environment
variable is set on invocation, $ENV is sourced after the profile
scripts.  The value of ENV is subjected to parameter expansion, command
substitution, and arithmetic expansion before being interpreted as a
pathname.  Note that the PRIVILEGED option also affects the execution
of startup files.

The following options are set if the shell is invoked as sh or ksh:
NO_BAD_PATTERN, NO_BANG_HIST, NO_BG_NICE, NO_EQUALS,
NO_FUNCTION_ARGZERO, GLOB_SUBST, NO_GLOBAL_EXPORT, NO_HUP,
INTERACTIVE_COMMENTS, KSH_ARRAYS, NO_MULTIOS, NO_NOMATCH, NO_NOTIFY,
POSIX_BUILTINS, NO_PROMPT_PERCENT, RM_STAR_SILENT, SH_FILE_EXPANSION,
SH_GLOB, SH_OPTION_LETTERS, SH_WORD_SPLIT.  Additionally the BSD_ECHO
and IGNORE_BRACES options are set if zsh is invoked as sh.  Also, the
KSH_OPTION_PRINT, LOCAL_OPTIONS, PROMPT_BANG, PROMPT_SUBST and
SINGLE_LINE_ZLE options are set if zsh is invoked as ksh.

Please note that, whilst reasonable efforts are taken to address
incompatibilities when they arise, zsh does not guarantee complete
emulation of other shells, nor POSIX compliance. For more information on
the differences between zsh and other shells, please refer to chapterĀ 2
of the shell FAQ, `https://www.zsh.org/FAQ/'.


File: zsh.info,  Node: Restricted Shell,  Prev: Compatibility,  Up: Invocation

4.3 Restricted Shell
====================

When the basename of the command used to invoke zsh starts with the
letter `r' or the `-r' command line option is supplied at invocation,
the shell becomes restricted.  Emulation mode is determined after
stripping the letter `r' from the invocation name.  The following are
disabled in restricted mode:


   * changing directories with the cd builtin

   * changing or unsetting the EGID, EUID, GID, HISTFILE, HISTSIZE,
     IFS, LD_AOUT_LIBRARY_PATH, LD_AOUT_PRELOAD, LD_LIBRARY_PATH,
     LD_PRELOAD, MODULE_PATH, module_path, PATH, path, SHELL, UID and
     USERNAME parameters

   * specifying command names containing /

   * specifying command pathnames using hash

   * redirecting output to files

   * using the exec builtin command to replace the shell with another
     command

   * using jobs -Z to overwrite the shell process' argument and
     environment space

   * using the ARGV0 parameter to override argv[0] for external commands

   * turning off restricted mode with set +r or unsetopt RESTRICTED

These restrictions are enforced after processing the startup files.  The
startup files should set up PATH to point to a directory of commands
which can be safely invoked in the restricted environment.  They may
also add further restrictions by disabling selected builtins.

Restricted mode can also be activated any time by setting the
RESTRICTED option.  This immediately enables all the restrictions
described above even if the shell still has not processed all startup
files.

A shell _Restricted Mode_ is an outdated way to restrict what users may
do:  modern systems have better, safer and more reliable ways to
confine user actions, such as _chroot jails_, _containers_ and _zones_.

A restricted shell is very difficult to implement safely.  The feature
may be removed in a future version of zsh.

It is important to realise that the restrictions only apply to the
shell, not to the commands it runs (except for some shell builtins).
While a restricted shell can only run the restricted list of commands
accessible via the predefined `PATH' variable, it does not prevent those
commands from running any other command.

As an example, if `env' is among the list of _allowed_ commands, then
it allows the user to run any command as `env' is not a shell builtin
command and can run arbitrary executables.

So when implementing a restricted shell framework it is important to be
fully aware of what actions each of the _allowed_ commands or features
(which may be regarded as _modules_) can perform.

Many commands can have their behaviour affected by environment
variables.  Except for the few listed above, zsh does not restrict the
setting of environment variables.

If a `perl', `python', `bash', or other general purpose interpreted
script is treated as a restricted command, the user can work around the
restriction by setting specially crafted `PERL5LIB', `PYTHONPATH',
`BASHENV' (etc.) environment variables. On GNU systems, any command can
be made to run arbitrary code when performing character set conversion
(including zsh itself) by setting a `GCONV_PATH' environment variable.
Those are only a few examples.

Bear in mind that, contrary to some other shells, `readonly' is not a
security feature in zsh as it can be undone and so cannot be used to
mitigate the above.

A restricted shell only works if the allowed commands are few and
carefully written so as not to grant more access to users than
intended.  It is also important to restrict what zsh module the user may
load as some of them, such as `zsh/system', `zsh/mapfile' and
`zsh/files', allow bypassing most of the restrictions.


File: zsh.info,  Node: Files,  Next: Shell Grammar,  Prev: Invocation,  Up: Top

5 Files
*******



5.1 Startup/Shutdown Files
==========================

Commands are first read from /etc/zshenv; this cannot be overridden.
Subsequent behaviour is modified by the RCS and GLOBAL_RCS options; the
former affects all startup files, while the second only affects global
startup files (those shown here with a path starting with a /).  If one
of the options is unset at any point, any subsequent startup file(s) of
the corresponding type will not be read.  It is also possible for a
file in $ZDOTDIR to re-enable GLOBAL_RCS. Both RCS and GLOBAL_RCS are
set by default.

Commands are then read from $ZDOTDIR/.zshenv.  If the shell is a login
shell, commands are read from /etc/zprofile and then $ZDOTDIR/.zprofile.  Then,
if the shell is interactive, commands are read from /etc/zshrc and then
$ZDOTDIR/.zshrc.  Finally, if the shell is a login shell, /etc/zlogin
and $ZDOTDIR/.zlogin are read.

When a login shell exits, the files $ZDOTDIR/.zlogout and then
/etc/zlogout are read.  This happens with either an explicit exit via
the exit or logout commands, or an implicit exit by reading end-of-file
from the terminal.  However, if the shell terminates due to exec'ing
another process, the logout files are not read.  These are also
affected by the RCS and GLOBAL_RCS options.  Note also that the RCS
option affects the saving of history files, i.e. if RCS is unset when
the shell exits, no history file will be saved.

If ZDOTDIR is unset, HOME is used instead.  Files listed above as being
in /etc may be in another directory, depending on the installation.

As /etc/zshenv is run for all instances of zsh, it is important that it
be kept as small as possible.  In particular, it is a good idea to put
code that does not need to be run for every single shell behind a test
of the form `if [[ -o rcs ]]; then ...' so that it will not be executed
when zsh is invoked with the `-f' option.

5.2 Files
=========


$ZDOTDIR/.zshenv

$ZDOTDIR/.zprofile

$ZDOTDIR/.zshrc

$ZDOTDIR/.zlogin

$ZDOTDIR/.zlogout

${TMPPREFIX}*   (default is /tmp/zsh*)

/etc/zshenv

/etc/zprofile

/etc/zshrc

/etc/zlogin

/etc/zlogout    (installation-specific - /etc is the default)


Any of these files may be pre-compiled with the zcompile builtin
command (*Note Shell Builtin Commands::).  If a compiled file exists
(named for the original file plus the .zwc extension) and it is newer
than the original file, the compiled file will be used instead.


File: zsh.info,  Node: Shell Grammar,  Next: Redirection,  Prev: Files,  Up: Top

6 Shell Grammar
***************



* Menu:

* Simple Commands & Pipelines::
* Precommand Modifiers::
* Complex Commands::
* Alternate Forms For Complex Commands::
* Reserved Words::
* Errors::
* Comments::
* Aliasing::
* Quoting::


File: zsh.info,  Node: Simple Commands & Pipelines,  Next: Precommand Modifiers,  Up: Shell Grammar

6.1 Simple Commands & Pipelines
===============================

A _simple command_ is a sequence of optional parameter assignments
followed by blank-separated words, with optional redirections
interspersed.  For a description of assignment, see the beginning of
*Note Parameters::.

The first word is the command to be executed, and the remaining words,
if any, are arguments to the command.  If a command name is given, the
parameter assignments modify the environment of the command when it is
executed.  The value of a simple command is its exit status, or 128
plus the signal number if terminated by a signal.  For example,


     echo foo

is a simple command with arguments.

A _pipeline_ is either a simple command, or a sequence of two or more
simple commands where each command is separated from the next by `|' or
`|&'.  Where commands are separated by `|', the standard output of the
first command is connected to the standard input of the next.  `|&' is
shorthand for `2>&1 |', which connects both the standard output and the
standard error of the command to the standard input of the next.  The
value of a pipeline is the value of the last command, unless the
pipeline is preceded by `!' in which case the value is the logical
inverse of the value of the last command.  For example,


     echo foo | sed 's/foo/bar/'

is a pipeline, where the output (`foo' plus a newline) of the first
command will be passed to the input of the second.

If a pipeline is preceded by `coproc', it is executed as a coprocess; a
two-way pipe is established between it and the parent shell.  The shell
can read from or write to the coprocess by means of the `>&p' and `<&p'
redirection operators or with `print -p' and `read -p'.  A pipeline
cannot be preceded by both `coproc' and `!'.  If job control is active,
the coprocess can be treated in other than input and output as an
ordinary background job.

A _sublist_ is either a single pipeline, or a sequence of two or more
pipelines separated by `&&' or `||'.  If two pipelines are separated by
`&&', the second pipeline is executed only if the first succeeds
(returns a zero status).  If two pipelines are separated by `||', the
second is executed only if the first fails (returns a nonzero status).
Both operators have equal precedence and are left associative.  The
value of the sublist is the value of the last pipeline executed.  For
example,


     dmesg | grep panic && print yes

is a sublist consisting of two pipelines, the second just a simple
command which will be executed if and only if the grep command returns
a zero status.  If it does not, the value of the sublist is that return
status, else it is the status returned by the print (almost certainly
zero).

A _list_ is a sequence of zero or more sublists, in which each sublist
is terminated by `;', `&', `&|', `&!', or a newline.  This terminator
may optionally be omitted from the last sublist in the list when the
list appears as a complex command inside `(...)'  or `{...}'.  When a
sublist is terminated by `;' or newline, the shell waits for it to
finish before executing the next sublist.  If a sublist is terminated
by a `&', `&|', or `&!', the shell executes the last pipeline in it in
the background, and does not wait for it to finish (note the difference
from other shells which execute the whole sublist in the background).
A backgrounded pipeline returns a status of zero.

More generally, a list can be seen as a set of any shell commands
whatsoever, including the complex commands below; this is implied
wherever the word `list' appears in later descriptions.  For example,
the commands in a shell function form a special sort of list.


File: zsh.info,  Node: Precommand Modifiers,  Next: Complex Commands,  Prev: Simple Commands & Pipelines,  Up: Shell Grammar

6.2 Precommand Modifiers
========================

A simple command may be preceded by a _precommand modifier_, which will
alter how the command is interpreted.  These modifiers are shell
builtin commands with the exception of nocorrect which is a reserved
word.


-
     The command is executed with a `-' prepended to its argv[0] string.

builtin
     The command word is taken to be the name of a builtin command,
     rather than a shell function or external command.

command [ -pvV ]
     The command word is taken to be the name of an external command,
     rather than a shell function or builtin.   If the POSIX_BUILTINS
     option is set, builtins will also be executed but certain special
     properties of them are suppressed. The -p flag causes a default
     path to be searched instead of that in $path. With the -v flag,
     command is similar to whence and with -V, it is equivalent to
     whence -v.

exec [ -cl ] [ -a ARGV0 ]
     The following command together with any arguments is run in place
     of the current process, rather than as a sub-process.  The shell
     does not fork and is replaced.  The shell does not invoke
     TRAPEXIT, nor does it source zlogout files.  The options are
     provided for compatibility with other shells.

     The -c option clears the environment.

     The -l option is equivalent to the - precommand modifier, to treat
     the replacement command as a login shell; the command is executed
     with a - prepended to its argv[0] string.  This flag has no effect
     if used together with the -a option.

     The -a option is used to specify explicitly the argv[0] string
     (the name of the command as seen by the process itself) to be used
     by the replacement command and is directly equivalent to setting a
     value for the ARGV0 environment variable.

nocorrect
     Spelling correction is not done on any of the words.  This must
     appear before any other precommand modifier, as it is interpreted
     immediately, before any parsing is done.  It has no effect in
     non-interactive shells.

noglob
     Filename generation (globbing) is not performed on any of the
     words.



File: zsh.info,  Node: Complex Commands,  Next: Alternate Forms For Complex Commands,  Prev: Precommand Modifiers,  Up: Shell Grammar

6.3 Complex Commands
====================

A _complex command_ in zsh is one of the following:


if LIST then LIST [ elif LIST then LIST ] ... [ else LIST ] fi
     The if LIST is executed, and if it returns a zero exit status, the
     then LIST is executed.  Otherwise, the elif LIST is executed and
     if its status is zero, the then LIST is executed.  If each elif
     LIST returns nonzero status, the else LIST is executed.

for NAME ... [ in WORD ... ] TERM do LIST done
     Expand the list of WORDs, and set the parameter NAME to each of
     them in turn, executing LIST each time.  If the `in WORD' is
     omitted, use the positional parameters instead of the WORDs.

     The TERM consists of one or more newline or ; which terminate the
     WORDs, and are optional when the `in WORD' is omitted.

     More than one parameter NAME can appear before the list of WORDs.
     If N NAMEs are given, then on each execution of the loop the next
     N WORDs are assigned to the corresponding parameters.  If there
     are more NAMEs than remaining WORDs, the remaining parameters are
     each set to the empty string.  Execution of the loop ends when
     there is no remaining WORD to assign to the first NAME.  It is
     only possible for in to appear as the first NAME in the list, else
     it will be treated as marking the end of the list.

for (( [EXPR1] ; [EXPR2] ; [EXPR3] )) do LIST done
     The arithmetic expression EXPR1 is evaluated first (see *Note
     Arithmetic Evaluation::).  The arithmetic expression EXPR2 is
     repeatedly evaluated until it evaluates to zero and when non-zero,
     LIST is executed and the arithmetic expression EXPR3 evaluated.
     If any expression is omitted, then it behaves as if it evaluated
     to 1.

while LIST do LIST done
     Execute the do LIST as long as the while LIST returns a zero exit
     status.

until LIST do LIST done
     Execute the do LIST as long as until LIST returns a nonzero exit
     status.

repeat WORD do LIST done
     WORD is expanded and treated as an arithmetic expression, which
     must evaluate to a number N.  LIST is then executed N times.

     The repeat syntax is disabled by default when the shell starts in
     a mode emulating another shell.  It can be enabled with the
     command `enable -r repeat'

case WORD in [ [(] PATTERN [ | PATTERN ] ... ) LIST (;;|;&|;|) ] ... esac
     Execute the LIST associated with the first PATTERN that matches
     WORD, if any.  The form of the patterns is the same as that used
     for filename generation.  See *Note Filename Generation::.

     Note further that, unless the SH_GLOB option is set, the whole
     pattern with alternatives is treated by the shell as equivalent to
     a group of patterns within parentheses, although white space may
     appear about the parentheses and the vertical bar and will be
     stripped from the pattern at those points.  White space may appear
     elsewhere in the pattern; this is not stripped.  If the SH_GLOB
     option is set, so that an opening parenthesis can be unambiguously
     treated as part of the case syntax, the expression is parsed into
     separate words and these are treated as strict alternatives (as in
     other shells).

     If the LIST that is executed is terminated with ;& rather than ;;,
     the following list is also executed.  The rule for the terminator
     of the following list ;;, ;& or ;| is applied unless the esac is
     reached.

     If the LIST that is executed is terminated with ;| the shell
     continues to scan the PATTERNs looking for the next match,
     executing the corresponding LIST, and applying the rule for the
     corresponding terminator ;;, ;& or ;|.  Note that WORD is not
     re-expanded; all applicable PATTERNs are tested with the same WORD.

select NAME [ in WORD ... TERM ] do LIST done
     where TERM is one or more newline or ; to terminate the WORDs.  Print
     the set of WORDs, each preceded by a number.  If the in WORD is
     omitted, use the positional parameters.  The PROMPT3 prompt is
     printed and a line is read from the line editor if the shell is
     interactive and that is active, or else standard input.  If this
     line consists of the number of one of the listed WORDs, then the
     parameter NAME is set to the WORD corresponding to this number.
     If this line is empty, the selection list is printed again.
     Otherwise, the value of the parameter NAME is set to null.  The
     contents of the line read from standard input is saved in the
     parameter REPLY.  LIST is executed for each selection until a
     break or end-of-file is encountered.

( LIST )
     Execute LIST in a subshell.  Traps set by the trap builtin are
     reset to their default values while executing LIST; an exception
     is that ignored signals will continue to be ignored if the option
     POSIXTRAPS is set.

{ LIST }
     Execute LIST.

{ TRY-LIST } always { ALWAYS-LIST }
     First execute TRY-LIST.  Regardless of errors, or break or
     continue commands encountered within TRY-LIST, execute
     ALWAYS-LIST.  Execution then continues from the result of the
     execution of TRY-LIST; in other words, any error, or break or
     continue command is treated in the normal way, as if ALWAYS-LIST
     were not present.  The two chunks of code are referred to as the
     `try block' and the `always block'.

     Optional newlines or semicolons may appear after the always; note,
     however, that they may _not_ appear between the preceding closing
     brace and the always.

     An `error' in this context is a condition such as a syntax error
     which causes the shell to abort execution of the current function,
     script, or list.  Syntax errors encountered while the shell is
     parsing the code do not cause the ALWAYS-LIST to be executed.  For
     example, an erroneously constructed if block in TRY-LIST would
     cause the shell to abort during parsing, so that ALWAYS-LIST would
     not be executed, while an erroneous substitution such as ${*foo*}
     would cause a run-time error, after which ALWAYS-LIST would be
     executed.

     An error condition can be tested and reset with the special integer
     variable TRY_BLOCK_ERROR.  Outside an ALWAYS-LIST the value is
     irrelevant, but it is initialised to -1.  Inside ALWAYS-LIST, the
     value is 1 if an error occurred in the TRY-LIST, else 0.  If
     TRY_BLOCK_ERROR is set to 0 during the ALWAYS-LIST, the error
     condition caused by the TRY-LIST is reset, and shell execution
     continues normally after the end of ALWAYS-LIST.  Altering the
     value during the TRY-LIST is not useful (unless this forms part of
     an enclosing always block).

     Regardless of TRY_BLOCK_ERROR, after the end of ALWAYS-LIST the
     normal shell status $? is the value returned from TRY-LIST.  This
     will be non-zero if there was an error, even if TRY_BLOCK_ERROR
     was set to zero.

     The following executes the given code, ignoring any errors it
     causes.  This is an alternative to the usual convention of
     protecting code by executing it in a subshell.


          {
              # code which may cause an error
            } always {
              # This code is executed regardless of the error.
              (( TRY_BLOCK_ERROR = 0 ))
          }
          # The error condition has been reset.

     When a try block occurs outside of any function, a return or a
     exit encountered in TRY-LIST does _not_ cause the execution of
     ALWAYS-LIST.  Instead, the shell exits immediately after any EXIT
     trap has been executed.  Otherwise, a return command encountered
     in TRY-LIST will cause the execution of ALWAYS-LIST, just like
     break and continue.

     

function [ -T ] WORD ... [ () ] [ TERM ] { LIST }
WORD ... () [ TERM ] { LIST }
WORD ... () [ TERM ] COMMAND
     where TERM is one or more newline or ;.  Define a function which
     is referenced by any one of WORD.  Normally, only one WORD is
     provided; multiple WORDs are usually only useful for setting traps.
     The body of the function is the LIST between the { and }.  See
     *Note Functions::.

     The options of function have the following meanings:


    -T
          Enable tracing for this function, as though with functions
          -T.  See the documentation of the -f option to the typeset
          builtin, in *Note Shell Builtin Commands::.


     If the option SH_GLOB is set for compatibility with other shells,
     then whitespace may appear between the left and right parentheses
     when there is a single WORD;  otherwise, the parentheses will be
     treated as forming a globbing pattern in that case.

     In any of the forms above, a redirection may appear outside the
     function body, for example


          func() { ... } 2>&1

     The redirection is stored with the function and applied whenever
     the function is executed.  Any variables in the redirection are
     expanded at the point the function is executed, but outside the
     function scope.

time [ PIPELINE ]
     The PIPELINE is executed, and timing statistics are reported on
     the standard error in the form specified by the TIMEFMT parameter.
     If PIPELINE is omitted, print statistics about the shell process
     and its children.

[[ EXP ]]
     Evaluates the conditional expression EXP and return a zero exit
     status if it is true.  See *Note Conditional Expressions:: for a
     description of EXP.



File: zsh.info,  Node: Alternate Forms For Complex Commands,  Next: Reserved Words,  Prev: Complex Commands,  Up: Shell Grammar

6.4 Alternate Forms For Complex Commands
========================================

Many of zsh's complex commands have alternate forms.  These are
non-standard and are likely not to be obvious even to seasoned shell
programmers; they should not be used anywhere that portability of shell
code is a concern.

The short versions below only work if SUBLIST is of the form `{ LIST }'
or if the SHORT_LOOPS option is set.  For the if, while and until
commands, in both these cases the test part of the loop must also be
suitably delimited, such as by `[[ ... ]]' or `(( ... ))', else the end
of the test will not be recognized.  For the for, repeat, case and
select commands no such special form for the arguments is necessary,
but the other condition (the special form of SUBLIST or use of the
SHORT_LOOPS option) still applies.  The SHORT_REPEAT option is
available to enable the short version only for the repeat command.


if LIST { LIST } [ elif LIST { LIST } ] ... [ else { LIST } ]
     An alternate form of if.  The rules mean that


          if [[ -o ignorebraces ]] {
            print yes
          }

     works, but


          if true {  # Does not work!
            print yes
          }

     does _not_, since the test is not suitably delimited.

if LIST SUBLIST
     A short form of the alternate if.  The same limitations on the
     form of LIST apply as for the previous form.

for NAME ... ( WORD ... ) SUBLIST
     A short form of for.

for NAME ... [ in WORD ... ] TERM SUBLIST
     where TERM is at least one newline or ;.  Another short form of
     for.

for (( [EXPR1] ; [EXPR2] ; [EXPR3] )) SUBLIST
     A short form of the arithmetic for command.

foreach NAME ... ( WORD ... ) LIST end
     Another form of for.

while LIST { LIST }
     An alternative form of while.  Note the limitations on the form of
     LIST mentioned above.

until LIST { LIST }
     An alternative form of until.  Note the limitations on the form of
     LIST mentioned above.

repeat WORD SUBLIST
     This is a short form of repeat.

case WORD { [ [(] PATTERN [ | PATTERN ] ... ) LIST (;;|;&|;|) ] ... }
     An alternative form of case.

select NAME [ in WORD ... TERM ] SUBLIST
     where TERM is at least one newline or ;.  A short form of select.

function WORD ... [ () ] [ TERM ] SUBLIST
     This is a short form of function.



File: zsh.info,  Node: Reserved Words,  Next: Errors,  Prev: Alternate Forms For Complex Commands,  Up: Shell Grammar

6.5 Reserved Words
==================

The following words are recognized as reserved words when used as the
first word of a command unless quoted or disabled using disable -r:

do done esac then elif else fi for case if while function repeat time
until select coproc nocorrect foreach end ! [[ { } declare export float
integer local readonly typeset

Additionally, `}' is recognized in any position if neither the
IGNORE_BRACES option nor the IGNORE_CLOSE_BRACES option is set.


File: zsh.info,  Node: Errors,  Next: Comments,  Prev: Reserved Words,  Up: Shell Grammar

6.6 Errors
==========

Certain errors are treated as fatal by the shell: in an interactive
shell, they cause control to return to the command line, and in a
non-interactive shell they cause the shell to be aborted.  In older
versions of zsh, a non-interactive shell running a script would not
abort completely, but would resume execution at the next command to be
read from the script, skipping the remainder of any functions or shell
constructs such as loops or conditions; this somewhat illogical
behaviour can be recovered by setting the option CONTINUE_ON_ERROR.

Fatal errors found in non-interactive shells include:


   * Failure to parse shell options passed when invoking the shell

   * Failure to change options with the set builtin

   * Parse errors of all sorts, including failures to parse
     mathematical expressions

   * Failures to set or modify variable behaviour with typeset, local,
     declare, export, integer, float

   * Execution of incorrectly positioned loop control structures
     (continue, break)

   * Attempts to use regular expression with no regular expression
     module available

   * Disallowed operations when the RESTRICTED options is set

   * Failure to create a pipe needed for a pipeline

   * Failure to create a multio

   * Failure to autoload a module needed for a declared shell feature

   * Errors creating command or process substitutions

   * Syntax errors in glob qualifiers

   * File generation errors where not caught by the option BAD_PATTERN

   * All bad patterns used for matching within case statements

   * File generation failures where not caused by NOMATCH or similar
     options

   * All file generation errors where the pattern was used to create a
     multio

   * Memory errors where detected by the shell

   * Invalid subscripts to shell variables

   * Attempts to assign read-only variables

   * Logical errors with variables such as assignment to the wrong type

   * Use of invalid variable names

   * Errors in variable substitution syntax

   * Failure to convert characters in $'...' expressions

If the POSIX_BUILTINS option is set, more errors associated with shell
builtin commands are treated as fatal, as specified by the POSIX
standard.




File: zsh.info,  Node: Comments,  Next: Aliasing,  Prev: Errors,  Up: Shell Grammar

6.7 Comments
============

In non-interactive shells, or in interactive shells with the
INTERACTIVE_COMMENTS option set, a word beginning with the third
character of the histchars parameter (`#' by default) causes that word
and all the following characters up to a newline to be ignored.


File: zsh.info,  Node: Aliasing,  Next: Quoting,  Prev: Comments,  Up: Shell Grammar

6.8 Aliasing
============

Every eligible _word_ in the shell input is checked to see if there is
an alias defined for it.  If so, it is replaced by the text of the
alias if it is in command position (if it could be the first word of a
simple command), or if the alias is global.  If the replacement text
ends with a space, the next word in the shell input is always eligible
for purposes of alias expansion.

It is an error for the function name, WORD, in the sh-compatible
function definition syntax `WORD () ...' to be a word that resulted
from alias expansion, unless the ALIAS_FUNC_DEF option is set.

An alias is defined using the alias builtin; global aliases may be
defined using the -g option to that builtin.

A _word_ is defined as:


   * Any plain string or glob pattern

   * Any quoted string, using any quoting method (note that the quotes
     must be part of the alias definition for this to be eligible)

   * Any parameter reference or command substitution

   * Any series of the foregoing, concatenated without whitespace or
     other tokens between them

   * Any reserved word (case, do, else, etc.)

   * With global aliasing, any command separator, any redirection
     operator, and `(' or `)' when not part of a glob pattern

Alias expansion is done on the shell input before any other expansion
except history expansion.  Therefore, if an alias is defined for the
word foo, alias expansion may be avoided by quoting part of the word,
e.g. \foo.  Any form of quoting works, although there is nothing to
prevent an alias being defined for the quoted form such as \foo as well.

In particular, note that quoting must be used when using unalias to
remove global aliases:


     % alias -g foo=bar
     % unalias foo
     unalias: no such hash table element: bar
     % unalias \foo
     %

When POSIX_ALIASES is set, only plain unquoted strings are eligible for
aliasing.  The alias builtin does not reject ineligible aliases, but
they are not expanded.

For use with completion, which would remove an initial backslash
followed by a character that isn't special, it may be more convenient
to quote the word by starting with a single quote, i.e. 'foo;
completion will automatically add the trailing single quote.



6.8.1 Alias difficulties
------------------------

Although aliases can be used in ways that bend normal shell syntax, not
every string of non-white-space characters can be used as an alias.

Any set of characters not listed as a word above is not a word, hence no
attempt is made to expand it as an alias, no matter how it is defined
(i.e. via the builtin or the special parameter aliases described in
*Note The zsh/parameter Module::).  However, as noted in the case of
POSIX_ALIASES above, the shell does not attempt to deduce whether the
string corresponds to a word at the time the alias is created.

For example, an expression containing an = at the start of a command
line is an assignment and cannot be expanded as an alias; a lone = is
not an assignment but can only be set as an alias using the parameter,
as otherwise the = is taken part of the syntax of the builtin command.

It is not presently possible to alias the `((' token that introduces
arithmetic expressions, because until a full statement has been parsed,
it cannot be distinguished from two consecutive `(' tokens introducing
nested subshells.  Also, if a separator such as && is aliased, \&&
turns into the two tokens \& and &, each of which may have been aliased
separately.  Similarly for \<<, \>|, etc.

There is a commonly encountered problem with aliases illustrated by the
following code:


     alias echobar='echo bar'; echobar

This prints a message that the command echobar could not be found.
This happens because aliases are expanded when the code is read in; the
entire line is read in one go, so that when echobar is executed it is
too late to expand the newly defined alias.  This is often a problem in
shell scripts, functions, and code executed with `source' or `.'.
Consequently, use of functions rather than aliases is recommended in
non-interactive code.




File: zsh.info,  Node: Quoting,  Prev: Aliasing,  Up: Shell Grammar

6.9 Quoting
===========

A character may be _quoted_ (that is, made to stand for itself) by
preceding it with a `\'.  `\' followed by a newline is ignored.

A string enclosed between `$'' and `'' is processed the same way as the
string arguments of the print builtin, and the resulting string is
considered to be entirely quoted.  A literal `'' character can be
included in the string by using the `\'' escape.

All characters enclosed between a pair of single quotes ('') that is
not preceded by a `$' are quoted.  A single quote cannot appear within
single quotes unless the option RC_QUOTES is set, in which case a pair
of single quotes are turned into a single quote.  For example,


     print ''''

outputs nothing apart from a newline if RC_QUOTES is not set, but one
single quote if it is set.

Inside double quotes (""), parameter and command substitution occur,
and `\' quotes the characters `\', ``', `"', `$', and the first
character of $histchars (default `!').


File: zsh.info,  Node: Redirection,  Next: Command Execution,  Prev: Shell Grammar,  Up: Top

7 Redirection
*************

If a command is followed by & and job control is not active, then the
default standard input for the command is the empty file /dev/null.
Otherwise, the environment for the execution of a command contains the
file descriptors of the invoking shell as modified by input/output
specifications.

The following may appear anywhere in a simple command or may precede or
follow a complex command.  Expansion occurs before WORD or DIGIT is
used except as noted below.  If the result of substitution on WORD
produces more than one filename, redirection occurs for each separate
filename in turn.


< WORD
     Open file WORD for reading as standard input.  It is an error to
     open a file in this fashion if it does not exist.

<> WORD
     Open file WORD for reading and writing as standard input.  If the
     file does not exist then it is created.

> WORD
     Open file WORD for writing as standard output.  If the file does
     not exist then it is created.  If the file exists, and the CLOBBER
     option is unset, this causes an error; otherwise, it is truncated
     to zero length.

>| WORD
>! WORD
     Same as >, except that the file is truncated to zero length if it
     exists, regardless of CLOBBER.

>> WORD
     Open file WORD for writing in append mode as standard output.  If
     the file does not exist, and the CLOBBER and APPEND_CREATE options
     are both unset, this causes an error; otherwise, the file is
     created.

>>| WORD
>>! WORD
     Same as >>, except that the file is created if it does not exist,
     regardless of CLOBBER and APPEND_CREATE.

<<[-] WORD
     The shell input is read up to a line that is the same as WORD, or
     to an end-of-file.  No parameter expansion, command substitution or
     filename generation is performed on WORD.  The resulting document,
     called a _here-document_, becomes the standard input.

     If any character of WORD is quoted with single or double quotes or
     a `\', no interpretation is placed upon the characters of the
     document.  Otherwise, parameter and command substitution occurs,
     `\' followed by a newline is removed, and `\' must be used to
     quote the characters `\', `$', ``' and the first character of WORD.

     Note that WORD itself does not undergo shell expansion.  Backquotes
     in WORD do not have their usual effect; instead they behave
     similarly to double quotes, except that the backquotes themselves
     are passed through unchanged.  (This information is given for
     completeness and it is not recommended that backquotes be used.)
     Quotes in the form $'...' have their standard effect of expanding
     backslashed references to special characters.

     If <<- is used, then all leading tabs are stripped from WORD and
     from the document.

<<< WORD
     Perform shell expansion on WORD and pass the result to standard
     input.  This is known as a _here-string_.  Compare the use of WORD
     in here-documents above, where WORD does not undergo shell
     expansion.  The result will have a trailing newline after it.

<& NUMBER
>& NUMBER
     The standard input/output is duplicated from file descriptor
     NUMBER (see dup2(2)).

<& -
>& -
     Close the standard input/output.

<& p
>& p
     The input/output from/to the coprocess is moved to the standard
     input/output.

>& WORD
&> WORD
     (Except where `>& WORD' matches one of the above syntaxes; `&>'
     can always be used to avoid this ambiguity.)  Redirects both
     standard output and standard error (file descriptor 2) in the
     manner of `> WORD'.  Note that this does _not_ have the same
     effect as `> WORD 2>&1' in the presence of multios (see the
     section below).

>&| WORD
>&! WORD
&>| WORD
&>! WORD
     Redirects both standard output and standard error (file descriptor
     2) in the manner of `>| WORD'.

>>& WORD
&>> WORD
     Redirects both standard output and standard error (file descriptor
     2) in the manner of `>> WORD'.

>>&| WORD
>>&! WORD
&>>| WORD
&>>! WORD
     Redirects both standard output and standard error (file descriptor
     2) in the manner of `>>| WORD'.


If one of the above is preceded by a digit, then the file descriptor
referred to is that specified by the digit instead of the default 0 or
1.  The order in which redirections are specified is significant.  The
shell evaluates each redirection in terms of the (_file descriptor_,
_file_) association at the time of evaluation.  For example:



     ... 1>FNAME 2>&1

first associates file descriptor 1 with file FNAME.  It then associates
file descriptor 2 with the file associated with file descriptor 1 (that
is, FNAME).  If the order of redirections were reversed, file
descriptor 2 would be associated with the terminal (assuming file
descriptor 1 had been) and then file descriptor 1 would be associated
with file FNAME.

The `|&' command separator described in *Note Simple Commands &
Pipelines:: is a shorthand for `2>&1 |'.

The various forms of process substitution, `<(LIST)', and `=(LIST)' for
input and `>(LIST)' for output, are often used together with
redirection.  For example, if WORD in an output redirection is of the
form `>(LIST)' then the output is piped to the command represented by
LIST.  See *Note Process Substitution::.

7.1 Opening file descriptors using parameters
=============================================



When the shell is parsing arguments to a command, and the shell option
IGNORE_BRACES is not set, a different form of redirection is allowed:
instead of a digit before the operator there is a valid shell identifier
enclosed in braces.  The shell will open a new file descriptor that is
guaranteed to be at least 10 and set the parameter named by the
identifier to the file descriptor opened.  No whitespace is allowed
between the closing brace and the redirection character.  For example:



     ... {myfd}>&1

This opens a new file descriptor that is a duplicate of file descriptor
1 and sets the parameter myfd to the number of the file descriptor,
which will be at least 10.  The new file descriptor can be written to
using the syntax >&$myfd.  The file descriptor remains open in subshells
and forked external executables.

The syntax {VARID}>&-, for example {myfd}>&-, may be used to close a
file descriptor opened in this fashion.  Note that the parameter given
by VARID must previously be set to a file descriptor in this case.

It is an error to open or close a file descriptor in this fashion when
the parameter is readonly.  However, it is not an error to read or
write a file descriptor using <&$PARAM or >&$PARAM if PARAM is readonly.

If the option CLOBBER is unset, it is an error to open a file
descriptor using a parameter that is already set to an open file
descriptor previously allocated by this mechanism.  Unsetting the
parameter before using it for allocating a file descriptor avoids the
error.

Note that this mechanism merely allocates or closes a file descriptor;
it does not perform any redirections from or to it.  It is usually
convenient to allocate a file descriptor prior to use as an argument to
exec.  The syntax does not in any case work when used around complex
commands such as parenthesised subshells or loops, where the opening
brace is interpreted as part of a command list to be executed in the
current shell.

The following shows a typical sequence of allocation, use, and closing
of a file descriptor:


     integer myfd
     exec {myfd}>~/logs/mylogfile.txt
     print This is a log message. >&$myfd
     exec {myfd}>&-

Note that the expansion of the variable in the expression >&$myfd
occurs at the point the redirection is opened.  This is after the
expansion of command arguments and after any redirections to the left
on the command line have been processed.

7.2 Multios
===========

If the user tries to open a file descriptor for writing more than once,
the shell opens the file descriptor as a pipe to a process that copies
its input to all the specified outputs, similar to `tee', provided the
MULTIOS option is set, as it is by default.  Thus:


     date >foo >bar

writes the date to two files, named `foo' and `bar'.  Note that a pipe
is an implicit redirection; thus


     date >foo | cat

writes the date to the file `foo', and also pipes it to cat.

Note that the shell opens all the files to be used in the multio process
immediately, not at the point they are about to be written.

Note also that redirections are always expanded in order.  This happens
regardless of the setting of the MULTIOS option, but with the option in
effect there are additional consequences. For example, the meaning of
the expression >&1 will change after a previous redirection:


     date >&1 >output

In the case above, the >&1 refers to the standard output at the start
of the line; the result is similar to the tee command.  However,
consider:


     date >output >&1

As redirections are evaluated in order, when the >&1 is encountered the
standard output is set to the file output and another copy of the
output is therefore sent to that file.  This is unlikely to be what is
intended.

If the MULTIOS option is set, the word after a redirection operator is
also subjected to filename generation (globbing).  Thus


     : > *

will truncate all files in the current directory, assuming there's at
least one.  (Without the MULTIOS option, it would create an empty file
called `*'.)  Similarly, you can do


     echo exit 0 >> *.sh

If the user tries to open a file descriptor for reading more than once,
the shell opens the file descriptor as a pipe to a process that copies
all the specified inputs to its output in the order specified, provided
the MULTIOS option is set.  It should be noted that each file is opened
immediately, not at the point where it is about to be read: this
behaviour differs from cat, so if strictly standard behaviour is
needed, cat should be used instead.

Thus


     sort <foo <fubar

or even


     sort <f{oo,ubar}

is equivalent to `cat foo fubar | sort'.

Expansion of the redirection argument occurs at the point the
redirection is opened, at the point described above for the expansion
of the variable in >&$myfd.

Note that a pipe is an implicit redirection; thus


     cat bar | sort <foo

is equivalent to `cat bar foo | sort' (note the order of the inputs).

If the MULTIOS option is _un_set, each redirection replaces the
previous redirection for that file descriptor.  However, all files
redirected to are actually opened, so


     echo Hello > bar > baz

when MULTIOS is unset will truncate `bar', and write `Hello' into `baz'.

There is a problem when an output multio is attached to an external
program.  A simple example shows this:


     cat file >file1 >file2
     cat file1 file2

Here, it is possible that the second `cat' will not display the full
contents of file1 and file2 (i.e. the original contents of file
repeated twice).

The reason for this is that the multios are spawned after the cat
process is forked from the parent shell, so the parent shell does not
wait for the multios to finish writing data.  This means the command as
shown can exit before file1 and file2 are completely written.  As a
workaround, it is possible to run the cat process as part of a job in
the current shell:


     { cat file } >file >file2

Here, the {...} job will pause to wait for both files to be written.



7.3 Redirections with no command
================================

When a simple command consists of one or more redirection operators and
zero or more parameter assignments, but no command name, zsh can behave
in several ways.

If the parameter NULLCMD is not set or the option CSH_NULLCMD is set,
an error is caused.  This is the `csh' behavior and CSH_NULLCMD is set
by default when emulating `csh'.

If the option SH_NULLCMD is set, the builtin `:' is inserted as a
command with the given redirections.  This is the default when emulating
`sh' or `ksh'.

Otherwise, if the parameter NULLCMD is set, its value will be used as a
command with the given redirections.  If both NULLCMD and READNULLCMD
are set, then the value of the latter will be used instead of that of
the former when the redirection is an input.  The default for NULLCMD
is `cat' and for READNULLCMD is `more'. Thus


     < file

shows the contents of file on standard output, with paging if that is a
terminal.  NULLCMD and READNULLCMD may refer to shell functions.




File: zsh.info,  Node: Command Execution,  Next: Functions,  Prev: Redirection,  Up: Top

8 Command Execution
*******************

If a command name contains no slashes, the shell attempts to locate it.
If there exists a shell function by that name, the function is invoked
as described in *Note Functions::.  If there exists a shell builtin by
that name, the builtin is invoked.

Otherwise, the shell searches each element of $path for a directory
containing an executable file by that name.

If execution fails: an error message is printed, and one of the
following values is returned.


127
     The search was unsuccessful.  The error message is `command not
     found: CMD'.

126
     The executable file has insufficient permissions, is a directory
     or special file, or is not a script and is in a format
     unrecognized by the operating system.  The exact conditions and
     error message are operating system-dependent; see execve(2).

If execution fails because the file is not in executable format, and
the file is not a directory, it is assumed to be a shell script.
/bin/sh is spawned to execute it.  If the program is a file beginning
with `#!', the remainder of the first line specifies an interpreter for
the program.  The shell will execute the specified interpreter on
operating systems that do not handle this executable format in the
kernel.

If no external command is found but a function command_not_found_handler
exists the shell executes this function with all command line
arguments.  The return status of the function becomes the status of the
command.  Note that the handler is executed in a subshell forked to
execute an external command, hence changes to directories, shell
parameters, etc. have no effect on the main shell.


File: zsh.info,  Node: Functions,  Next: Jobs & Signals,  Prev: Command Execution,  Up: Top

9 Functions
***********

Shell functions are defined with the function reserved word or the
special syntax `FUNCNAME ()'.  Shell functions are read in and stored
internally.  Alias names are resolved when the function is read.
Functions are executed like commands with the arguments passed as
positional parameters.  (See *Note Command Execution::.)

Functions execute in the same process as the caller and share all files
and present working directory with the caller.  A trap on EXIT set
inside a function is executed after the function completes in the
environment of the caller.

The return builtin is used to return from function calls.

Function identifiers can be listed with the functions builtin.  Functions
can be undefined with the unfunction builtin.

9.1 Autoloading Functions
=========================



A function can be marked as _undefined_ using the autoload builtin (or
`functions -u' or `typeset -fu').  Such a function has no body.  When
the function is first executed, the shell searches for its definition
using the elements of the fpath variable.  Thus to define functions for
autoloading, a typical sequence is:


     fpath=(~/myfuncs $fpath)
     autoload myfunc1 myfunc2 ...

The usual alias expansion during reading will be suppressed if the
autoload builtin or its equivalent is given the option -U. This is
recommended for the use of functions supplied with the zsh distribution.  Note
that for functions precompiled with the zcompile builtin command the
flag -U must be provided when the .zwc file is created, as the
corresponding information is compiled into the latter.

For each ELEMENT in fpath, the shell looks for three possible files,
the newest of which is used to load the definition for the function:


ELEMENT.zwc
     A file created with the zcompile builtin command, which is
     expected to contain the definitions for all functions in the
     directory named ELEMENT.  The file is treated in the same manner
     as a directory containing files for functions and is searched for
     the definition of the function.   If the definition is not found,
     the search for a definition proceeds with the other two
     possibilities described below.

     If ELEMENT already includes a .zwc extension (i.e. the extension
     was explicitly given by the user), ELEMENT is searched for the
     definition of the function without comparing its age to that of
     other files; in fact, there does not need to be any directory
     named ELEMENT without the suffix.  Thus including an element such
     as `/usr/local/funcs.zwc' in fpath will speed up the search for
     functions, with the disadvantage that functions included must be
     explicitly recompiled by hand before the shell notices any changes.

ELEMENT/FUNCTION.zwc
     A file created with zcompile, which is expected to contain the
     definition for FUNCTION.  It may include other function definitions
     as well, but those are neither loaded nor executed; a file found
     in this way is searched _only_ for the definition of FUNCTION.

ELEMENT/FUNCTION
     A file of zsh command text, taken to be the definition for
     FUNCTION.


In summary, the order of searching is, first, in the _parents of_
directories in fpath for the newer of either a compiled directory or a
directory in fpath; second, if more than one of these contains a
definition for the function that is sought, the leftmost in the fpath
is chosen; and third, within a directory, the newer of either a compiled
function or an ordinary function definition is used.

If the KSH_AUTOLOAD option is set, or the file contains only a simple
definition of the function, the file's contents will be executed.  This
will normally define the function in question, but may also perform
initialization, which is executed in the context of the function
execution, and may therefore define local parameters.  It is an error
if the function is not defined by loading the file.

Otherwise, the function body (with no surrounding `FUNCNAME() {...}')
is taken to be the complete contents of the file.  This form allows the
file to be used directly as an executable shell script.  If processing
of the file results in the function being re-defined, the function
itself is not re-executed.  To force the shell to perform
initialization and then call the function defined, the file should
contain initialization code (which will be executed then discarded) in
addition to a complete function definition (which will be retained for
subsequent calls to the function), and a call to the shell function,
including any arguments, at the end.

For example, suppose the autoload file func contains


     func() { print This is func; }
     print func is initialized

then `func; func' with KSH_AUTOLOAD set will produce both messages on
the first call, but only the message `This is func' on the second and
subsequent calls.  Without KSH_AUTOLOAD set, it will produce the
initialization message on the first call, and the other message on the
second and subsequent calls.

It is also possible to create a function that is not marked as
autoloaded, but which loads its own definition by searching fpath, by
using `autoload -X' within a shell function.  For example, the
following are equivalent:


     myfunc() {
       autoload -X
     }
     myfunc args...

and


     unfunction myfunc   # if myfunc was defined
     autoload myfunc
     myfunc args...

In fact, the functions command outputs `builtin autoload -X' as the
body of an autoloaded function.  This is done so that


     eval "$(functions)"

produces a reasonable result.  A true autoloaded function can be
identified by the presence of the comment `# undefined' in the body,
because all comments are discarded from defined functions.

To load the definition of an autoloaded function myfunc without
executing myfunc, use:


     autoload +X myfunc


9.2 Anonymous Functions
=======================



If no name is given for a function, it is `anonymous' and is handled
specially.  Either form of function definition may be used: a `()' with
no preceding name, or a `function' with an immediately following open
brace.  The function is executed immediately at the point of definition
and is not stored for future use.  The function name is set to `(anon)'.

Arguments to the function may be specified as words following the
closing brace defining the function, hence if there are none no
arguments (other than $0) are set.  This is a difference from the way
other functions are parsed: normal function definitions may be followed
by certain keywords such as `else' or `fi', which will be treated as
arguments to anonymous functions, so that a newline or semicolon is
needed to force keyword interpretation.

Note also that the argument list of any enclosing script or function is
hidden (as would be the case for any other function called at this
point).

Redirections may be applied to the anonymous function in the same
manner as to a current-shell structure enclosed in braces.  The main
use of anonymous functions is to provide a scope for local variables.
This is particularly convenient in start-up files as these do not
provide their own local variable scope.

For example,


     variable=outside
     function {
       local variable=inside
       print "I am $variable with arguments $*"
     } this and that
     print "I am $variable"

outputs the following:


     I am inside with arguments this and that
     I am outside

Note that function definitions with arguments that expand to nothing,
for example `name=; function $name { ... }', are not treated as
anonymous functions.  Instead, they are treated as normal function
definitions where the definition is silently discarded.



9.3 Special Functions
=====================

Certain functions, if defined, have special meaning to the shell.



9.3.1 Hook Functions
--------------------



For the functions below, it is possible to define an array that has the
same name as the function with `_functions' appended.  Any element in
such an array is taken as the name of a function to execute; it is
executed in the same context and with the same arguments and same
initial value of $?  as the basic function.  For example, if
$chpwd_functions is an array containing the values `mychpwd',
`chpwd_save_dirstack', then the shell attempts to execute the functions
`chpwd', `mychpwd' and `chpwd_save_dirstack', in that order.  Any
function that does not exist is silently ignored.  A function found by
this mechanism is referred to elsewhere as a _hook function_.  An error
in any function causes subsequent functions not to be run.  Note
further that an error in a precmd hook causes an immediately following
periodic function not to run (though it may run at the next
opportunity).


chpwd
     Executed whenever the current working directory is changed.

periodic
     If the parameter PERIOD is set, this function is executed every
     $PERIOD seconds, just before a prompt.  Note that if multiple
     functions are defined using the array periodic_functions only one
     period is applied to the complete set of functions, and the
     scheduled time is not reset if the list of functions is altered.
     Hence the set of functions is always called together.

precmd
     Executed before each prompt.  Note that precommand functions are
     not re-executed simply because the command line is redrawn, as
     happens, for example, when a notification about an exiting job is
     displayed.

preexec
     Executed just after a command has been read and is about to be
     executed.  If the history mechanism is active (regardless of
     whether the line was discarded from the history buffer), the
     string that the user typed is passed as the first argument,
     otherwise it is an empty string.  The actual command that will be
     executed (including expanded aliases) is passed in two different
     forms: the second argument is a single-line, size-limited version
     of the command (with things like function bodies elided); the
     third argument contains the full text that is being executed.

zshaddhistory
     Executed when a history line has been read interactively, but
     before it is executed.  The sole argument is the complete history
     line (so that any terminating newline will still be present).

     If any of the hook functions returns status 1 (or any non-zero
     value other than 2, though this is not guaranteed for future
     versions of the shell) the history line will not be saved,
     although it lingers in the history until the next line is
     executed, allowing you to reuse or edit it immediately.

     If any of the hook functions returns status 2 the history line
     will be saved on the internal history list, but not written to the
     history file.  In case of a conflict, the first non-zero status
     value is taken.

     A hook function may call `fc -p ...' to switch the history context
     so that the history is saved in a different file from that in the
     global HISTFILE parameter.  This is handled specially: the history
     context is automatically restored after the processing of the
     history line is finished.

     The following example function works with one of the options
     INC_APPEND_HISTORY or SHARE_HISTORY set, in order that the line is
     written out immediately after the history entry is added.  It first
     adds the history line to the normal history with the newline
     stripped, which is usually the correct behaviour.  Then it
     switches the history context so that the line will be written to a
     history file in the current directory.


          zshaddhistory() {
            print -sr -- ${1%%$'\n'}
            fc -p .zsh_local_history
          }

zshexit
     Executed at the point where the main shell is about to exit
     normally.  This is not called by exiting subshells, nor when the
     exec precommand modifier is used before an external command.
     Also, unlike TRAPEXIT, it is not called when functions exit.



9.3.2 Trap Functions
--------------------

The functions below are treated specially but do not have corresponding
hook arrays.


TRAPNAL
     If defined and non-null, this function will be executed whenever
     the shell catches a signal SIGNAL, where NAL is a signal name as
     specified for the kill builtin.  The signal number will be passed
     as the first parameter to the function.

     If a function of this form is defined and null, the shell and
     processes spawned by it will ignore SIGNAL.

     The return status from the function is handled specially.  If it is
     zero, the signal is assumed to have been handled, and execution
     continues normally.  Otherwise, the shell will behave as
     interrupted except that the return status of the trap is retained.

     Programs terminated by uncaught signals typically return the
     status 128 plus the signal number.  Hence the following causes the
     handler for SIGINT to print a message, then mimic the usual effect
     of the signal.


          TRAPINT() {
            print "Caught SIGINT, aborting."
            return $(( 128 + $1 ))
          }

     The functions TRAPZERR, TRAPDEBUG and TRAPEXIT are never executed
     inside other traps.

TRAPDEBUG
     If the option DEBUG_BEFORE_CMD is set (as it is by default),
     executed before each command; otherwise executed after each
     command.  See the description of the trap builtin in *Note Shell
     Builtin Commands:: for details of additional features provided in
     debug traps.

TRAPEXIT
     Executed when the shell exits, or when the current function exits
     if defined inside a function.  The value of $? at the start of
     execution is the exit status of the shell or the return status of
     the function exiting.

TRAPZERR
     Executed whenever a command has a non-zero exit status.  However,
     the function is not executed if the command occurred in a sublist
     followed by `&&' or `||'; only the final command in a sublist of
     this type causes the trap to be executed.  The function TRAPERR
     acts the same as TRAPZERR on systems where there is no SIGERR
     (this is the usual case).


The functions beginning `TRAP' may alternatively be defined with the
trap builtin:  this may be preferable for some uses.  Setting a trap
with one form removes any trap of the other form for the same signal;
removing a trap in either form removes all traps for the same signal.
The forms


     TRAPNAL() {
      # code
     }

('function traps') and


     trap '
      # code
     ' NAL

('list traps') are equivalent in most ways, the exceptions being the
following:


   * Function traps have all the properties of normal functions,
     appearing in the list of functions and being called with their own
     function context rather than the context where the trap was
     triggered.

   * The return status from function traps is special, whereas a return
     from a list trap causes the surrounding context to return with the
     given status.

   * Function traps are not reset within subshells, in accordance with
     zsh behaviour; list traps are reset, in accordance with POSIX
     behaviour.


File: zsh.info,  Node: Jobs & Signals,  Next: Arithmetic Evaluation,  Prev: Functions,  Up: Top

10 Jobs & Signals
*****************



10.1 Jobs
=========

If the MONITOR option is set, an interactive shell associates a _job_
with each pipeline.  It keeps a table of current jobs, printed by the
jobs command, and assigns them small integer numbers.  When a job is
started asynchronously with `&', the shell prints a line to standard
error which looks like:


     [1] 1234

indicating that the job which was started asynchronously was job number
1 and had one (top-level) process, whose process ID was 1234.

If a job is started with `&|' or `&!', then that job is immediately
disowned.  After startup, it does not have a place in the job table,
and is not subject to the job control features described here.

If you are running a job and wish to do something else you may hit the
key ^Z (control-Z) which sends a TSTP signal to the current job:  this
key may be redefined by the susp option of the external stty command.  The
shell will then normally indicate that the job has been `suspended',
and print another prompt.  You can then manipulate the state of this
job, putting it in the background with the bg command, or run some other
commands and then eventually bring the job back into the foreground with the
foreground command fg.  A ^Z takes effect immediately and is like an
interrupt in that pending output and unread input are discarded when it
is typed.

A job being run in the background will suspend if it tries to read from
the terminal.

Note that if the job running in the foreground is a shell function,
then suspending it will have the effect of causing the shell to fork.
This is necessary to separate the function's state from that of the
parent shell performing the job control, so that the latter can return
to the command line prompt.  As a result, even if fg is used to
continue the job the function will no longer be part of the parent
shell, and any variables set by the function will not be visible in the
parent shell.  Thus the behaviour is different from the case where the
function was never suspended.  Zsh is different from many other shells
in this regard.

One additional side effect is that use of disown with a job created by
suspending shell code in this fashion is delayed: the job can only be
disowned once any process started from the parent shell has terminated.
At that point, the disowned job disappears silently from the job list.

The same behaviour is found when the shell is executing code as the
right hand side of a pipeline or any complex shell construct such as
if, for, etc., in order that the entire block of code can be managed as
a single job.  Background jobs are normally allowed to produce output,
but this can be disabled by giving the command `stty tostop'.  If you
set this tty option, then background jobs will suspend when they try to
produce output like they do when they try to read input.

When a command is suspended and continued later with the fg or wait
builtins, zsh restores tty modes that were in effect when it was
suspended.  This (intentionally) does not apply if the command is
continued via `kill -CONT', nor when it is continued with bg.

There are several ways to refer to jobs in the shell.  A job can be
referred to by the process ID of any process of the job or by one of
the following:


%NUMBER
     The job with the given number.

%STRING
     The last job whose command line begins with STRING.

%?STRING
     The last job whose command line contains STRING.

%%
     Current job.

%+
     Equivalent to `%%'.

%-
     Previous job.

The shell learns immediately whenever a process changes state.  It
normally informs you whenever a job becomes blocked so that no further
progress is possible.  If the NOTIFY option is not set, it waits until
just before it prints a prompt before it informs you.  All such
notifications are sent directly to the terminal, not to the standard
output or standard error.

When the monitor mode is on, each background job that completes
triggers any trap set for CHLD.

When you try to leave the shell while jobs are running or suspended,
you will be warned that `You have suspended (running) jobs'.  You may
use the jobs command to see what they are.  If you do this or
immediately try to exit again, the shell will not warn you a second
time; the suspended jobs will be terminated, and the running jobs will
be sent a SIGHUP signal, if the HUP option is set.  

To avoid having the shell terminate the running jobs, either use the
nohup(1) command or the disown builtin.

10.2 Signals
============

The INT and QUIT signals for an invoked command are ignored if the
command is followed by `&' and the MONITOR option is not active.  The
shell itself always ignores the QUIT signal.  Otherwise, signals have
the values inherited by the shell from its parent (but see the TRAPNAL
special functions in *Note Functions::).

Certain jobs are run asynchronously by the shell other than those
explicitly put into the background; even in cases where the shell would
usually wait for such jobs, an explicit exit command or exit due to the
option ERR_EXIT will cause the shell to exit without waiting.  Examples
of such asynchronous jobs are process substitution, see *Note Process
Substitution::, and the handler processes for multios, see the section
_Multios_ in *Note Redirection::.


File: zsh.info,  Node: Arithmetic Evaluation,  Next: Conditional Expressions,  Prev: Jobs & Signals,  Up: Top

11 Arithmetic Evaluation
************************

The shell can perform integer and floating point arithmetic, either
using the builtin let, or via a substitution of the form $((...)).  For
integers, the shell is usually compiled to use 8-byte precision where
this is available, otherwise precision is 4 bytes.  This can be tested,
for example, by giving the command `print - $(( 12345678901 ))'; if the
number appears unchanged, the precision is at least 8 bytes.  Floating
point arithmetic always uses the `double' type with whatever
corresponding precision is provided by the compiler and the library.

The let builtin command takes arithmetic expressions as arguments; each
is evaluated separately.  Since many of the arithmetic operators, as
well as spaces, require quoting, an alternative form is provided: for
any command which begins with a `((', all the characters until a
matching `))' are treated as a double-quoted expression and arithmetic
expansion performed as for an argument of let.  More precisely,
`((...))' is equivalent to `let "..."'.  The return status is 0 if the
arithmetic value of the expression is non-zero, 1 if it is zero, and 2
if an error occurred.

For example, the following statement


     (( val = 2 + 1 ))

is equivalent to


     let "val = 2 + 1"

both assigning the value 3 to the shell variable val and returning a
zero status.

Integers can be in bases other than 10.  A leading `0x' or `0X' denotes
hexadecimal and a leading `0b' or `0B' binary.  Integers may also be of
the form `BASE#N', where BASE is a decimal number between two and
thirty-six representing the arithmetic base and N is a number in that
base (for example, `16#ff' is 255 in hexadecimal).  The BASE# may also
be omitted, in which case base 10 is used.  For backwards compatibility
the form `[BASE]N' is also accepted.

An integer expression or a base given in the form `BASE#N' may contain
underscores (`_') after the leading digit for visual guidance; these
are ignored in computation.  Examples are 1_000_000 or 0xffff_ffff
which are equivalent to 1000000 and 0xffffffff respectively.

It is also possible to specify a base to be used for output in the form
`[#BASE]', for example `[#16]'.  This is used when outputting
arithmetical substitutions or when assigning to scalar parameters, but
an explicitly defined integer or floating point parameter will not be
affected.  If an integer variable is implicitly defined by an
arithmetic expression, any base specified in this way will be set as the
variable's output arithmetic base as if the option `-i BASE' to the
typeset builtin had been used.  The expression has no precedence and if
it occurs more than once in a mathematical expression, the last
encountered is used.  For clarity it is recommended that it appear at
the beginning of an expression.  As an example:


     typeset -i 16 y
     print $(( [#8] x = 32, y = 32 ))
     print $x $y

outputs first `8#40', the rightmost value in the given output base, and
then `8#40 16#20', because y has been explicitly declared to have
output base 16, while x (assuming it does not already exist) is
implicitly typed by the arithmetic evaluation, where it acquires the
output base 8.

The BASE may be replaced or followed by an underscore, which may itself
be followed by a positive integer (if it is missing the value 3 is
used).  This indicates that underscores should be inserted into the
output string, grouping the number for visual clarity.  The following
integer specifies the number of digits to group together.  For example:


     setopt cbases
     print $(( [#16_4] 65536 ** 2 ))

outputs `0x1_0000_0000'.

The feature can be used with floating point numbers, in which case the
base must be omitted; grouping is away from the decimal point.  For
example,


     zmodload zsh/mathfunc
     print $(( [#_] sqrt(1e7) ))

outputs `3_162.277_660_168_379_5' (the number of decimal places shown
may vary).

If the C_BASES option is set, hexadecimal numbers are output in the
standard C format, for example `0xFF' instead of the usual `16#FF'.  If
the option OCTAL_ZEROES is also set (it is not by default), octal
numbers will be treated similarly and hence appear as `077' instead of
`8#77'.  This option has no effect on the output of bases other than
hexadecimal and octal, and these formats are always understood on input.

When an output base is specified using the `[#BASE]' syntax, an
appropriate base prefix will be output if necessary, so that the value
output is valid syntax for input.  If the # is doubled, for example
`[##16]', then no base prefix is output.

Floating point constants are recognized by the presence of a decimal
point or an exponent.  The decimal point may be the first character of
the constant, but the exponent character e or E may not, as it will be
taken for a parameter name.  All numeric parts (before and after the
decimal point and in the exponent) may contain underscores after the
leading digit for visual guidance; these are ignored in computation.

An arithmetic expression uses nearly the same syntax and associativity
of expressions as in C.

In the native mode of operation, the following operators are supported
(listed in decreasing order of precedence):


+ - ! ~ ++ -
     unary plus/minus, logical NOT, complement, {pre,post}{in,de}crement

<< >>
     bitwise shift left, right

&
     bitwise AND

^
     bitwise XOR

|
     bitwise OR

**
     exponentiation

* / %
     multiplication, division, modulus (remainder)

+ -
     addition, subtraction

< > <= >=
     comparison

== !=
     equality and inequality

&&
     logical AND

|| ^^
     logical OR, XOR

? :
     ternary operator

= += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
     assignment

,
     comma operator

The operators `&&', `||', `&&=', and `||=' are short-circuiting, and
only one of the latter two expressions in a ternary operator is
evaluated.  Note the precedence of the bitwise AND, OR, and XOR
operators.

With the option C_PRECEDENCES the precedences (but no other properties)
of the operators are altered to be the same as those in most other
languages that support the relevant operators:


+ - ! ~ ++ -
     unary plus/minus, logical NOT, complement, {pre,post}{in,de}crement

**
     exponentiation

* / %
     multiplication, division, modulus (remainder)

+ -
     addition, subtraction

<< >>
     bitwise shift left, right

< > <= >=
     comparison

== !=
     equality and inequality

&
     bitwise AND

^
     bitwise XOR

|
     bitwise OR

&&
     logical AND

^^
     logical XOR

||
     logical OR

? :
     ternary operator

= += -= *= /= %= &= ^= |= <<= >>= &&= ||= ^^= **=
     assignment

,
     comma operator

Note the precedence of exponentiation in both cases is below that of
unary operators, hence `-3**2' evaluates as `9', not `-9'.  Use
parentheses where necessary: `-(3**2)'.  This is for compatibility with
other shells.

Mathematical functions can be called with the syntax `FUNC(ARGS)',
where the function decides if the ARGS is used as a string or a
comma-separated list of arithmetic expressions. The shell currently
defines no mathematical functions by default, but the module
zsh/mathfunc may be loaded with the zmodload builtin to provide
standard floating point mathematical functions.

An expression of the form `##X' where X is any character sequence such
as `a', `^A', or `\M-\C-x' gives the value of this character and an
expression of the form `#NAME' gives the value of the first character
of the contents of the parameter NAME.  Character values are according
to the character set used in the current locale; for multibyte
character handling the option MULTIBYTE must be set.  Note that this
form is different from `$#NAME', a standard parameter substitution
which gives the length of the parameter NAME.  `#\' is accepted instead
of `##', but its use is deprecated.

Named parameters and subscripted arrays can be referenced by name
within an arithmetic expression without using the parameter expansion
syntax.  For example,


     ((val2 = val1 * 2))

assigns twice the value of $val1 to the parameter named val2.

An internal integer representation of a named parameter can be
specified with the integer builtin.  Arithmetic evaluation is performed
on the value of each assignment to a named parameter declared integer
in this manner.  Assigning a floating point number to an integer
results in rounding towards zero.

Likewise, floating point numbers can be declared with the float
builtin; there are two types, differing only in their output format, as
described for the typeset builtin.  The output format can be bypassed
by using arithmetic substitution instead of the parameter substitution,
i.e. `${FLOAT}' uses the defined format, but `$((FLOAT))' uses a
generic floating point format.

Promotion of integer to floating point values is performed where
necessary.  In addition, if any operator which requires an integer
(`&', `|', `^', `<<', `>>' and their equivalents with assignment) is
given a floating point argument, it will be silently rounded towards
zero except for `~' which rounds down.

Users should beware that, in common with many other programming
languages but not software designed for calculation, the evaluation of
an expression in zsh is taken a term at a time and promotion of integers
to floating point does not occur in terms only containing integers.  A
typical result of this is that a division such as 6/8 is truncated, in
this being rounded towards 0.  The FORCE_FLOAT shell option can be used
in scripts or functions where floating point evaluation is required
throughout.

Scalar variables can hold integer or floating point values at different
times; there is no memory of the numeric type in this case.

If a variable is first assigned in a numeric context without previously
being declared, it will be implicitly typed as integer or float and
retain that type either until the type is explicitly changed or until
the end of the scope.  This can have unforeseen consequences.  For
example, in the loop


     for (( f = 0; f < 1; f += 0.1 )); do
     # use $f
     done

if f has not already been declared, the first assignment will cause it
to be created as an integer, and consequently the operation `f += 0.1'
will always cause the result to be truncated to zero, so that the loop
will fail.  A simple fix would be to turn the initialization into `f =
0.0'.  It is therefore best to declare numeric variables with explicit
types.


File: zsh.info,  Node: Conditional Expressions,  Next: Prompt Expansion,  Prev: Arithmetic Evaluation,  Up: Top

12 Conditional Expressions
**************************

A _conditional expression_ is used with the [[ compound command to test
attributes of files and to compare strings.  Each expression can be
constructed from one or more of the following unary or binary
expressions:


-a FILE
     true if FILE exists.

-b FILE
     true if FILE exists and is a block special file.

-c FILE
     true if FILE exists and is a character special file.

-d FILE
     true if FILE exists and is a directory.

-e FILE
     true if FILE exists.

-f FILE
     true if FILE exists and is a regular file.

-g FILE
     true if FILE exists and has its setgid bit set.

-h FILE
     true if FILE exists and is a symbolic link.

-k FILE
     true if FILE exists and has its sticky bit set.

-n STRING
     true if length of STRING is non-zero.

-o OPTION
     true if option named OPTION is on.  OPTION may be a single
     character, in which case it is a single letter option name.  (See
     *Note Specifying Options::.)

     When no option named OPTION exists, and the POSIX_BUILTINS option
     hasn't been set, return 3 with a warning.  If that option is set,
     return 1 with no warning.

-p FILE
     true if FILE exists and is a FIFO special file (named pipe).

-r FILE
     true if FILE exists and is readable by current process.

-s FILE
     true if FILE exists and has size greater than zero.

-t FD
     true if file descriptor number FD is open and associated with a
     terminal device.  (note: FD is not optional)

-u FILE
     true if FILE exists and has its setuid bit set.

-v VARNAME
     true if shell variable VARNAME is set.

-w FILE
     true if FILE exists and is writable by current process.

-x FILE
     true if FILE exists and is executable by current process.  If FILE
     exists and is a directory, then the current process has permission
     to search in the directory.

-z STRING
     true if length of STRING is zero.

-L FILE
     true if FILE exists and is a symbolic link.

-O FILE
     true if FILE exists and is owned by the effective user ID of this
     process.

-G FILE
     true if FILE exists and its group matches the effective group ID
     of this process.

-S FILE
     true if FILE exists and is a socket.

-N FILE
     true if FILE exists and its access time is not newer than its
     modification time.

FILE1 -nt FILE2
     true if FILE1 exists and is newer than FILE2.

FILE1 -ot FILE2
     true if FILE1 exists and is older than FILE2.

FILE1 -ef FILE2
     true if FILE1 and FILE2 exist and refer to the same file.

STRING = PATTERN
STRING == PATTERN
     true if STRING matches PATTERN.  The two forms are exactly
     equivalent.  The `=' form is the traditional shell syntax (and
     hence the only one generally used with the test and [ builtins);
     the `==' form provides compatibility with other sorts of computer
     language.

STRING != PATTERN
     true if STRING does not match PATTERN.

STRING =~ REGEXP
     true if STRING matches the regular expression REGEXP.  If the
     option RE_MATCH_PCRE is set REGEXP is tested as a PCRE regular
     expression using the zsh/pcre module, else it is tested as a POSIX
     extended regular expression using the zsh/regex module.  Upon
     successful match, some variables will be updated; no variables are
     changed if the matching fails.

     If the option BASH_REMATCH is not set the scalar parameter MATCH
     is set to the substring that matched the pattern and the integer
     parameters MBEGIN and MEND to the index of the start and end,
     respectively, of the match in STRING, such that if STRING is
     contained in variable var the expression `${var[$MBEGIN,$MEND]}'
     is identical to `$MATCH'.  The setting of the option KSH_ARRAYS is
     respected.  Likewise, the array match is set to the substrings
     that matched parenthesised subexpressions and the arrays mbegin
     and mend to the indices of the start and end positions,
     respectively, of the substrings within STRING.  The arrays are not
     set if there were no parenthesised subexpressions.  For example,
     if the string `a short string' is matched against the regular
     expression `s(...)t', then (assuming the option KSH_ARRAYS is not
     set) MATCH, MBEGIN and MEND are `short', 3 and 7, respectively,
     while match, mbegin and mend are single entry arrays containing
     the strings `hor', `4' and `6', respectively.

     If the option BASH_REMATCH is set the array BASH_REMATCH is set to
     the substring that matched the pattern followed by the substrings
     that matched parenthesised subexpressions within the pattern.

STRING1 < STRING2
     true if STRING1 comes before STRING2 based on ASCII value of their
     characters.

STRING1 > STRING2
     true if STRING1 comes after STRING2 based on ASCII value of their
     characters.

EXP1 -eq EXP2
     true if EXP1 is numerically equal to EXP2.  Note that for purely
     numeric comparisons use of the ((...)) builtin described in *Note
     Arithmetic Evaluation:: is more convenient than conditional
     expressions.

EXP1 -ne EXP2
     true if EXP1 is numerically not equal to EXP2.

EXP1 -lt EXP2
     true if EXP1 is numerically less than EXP2.

EXP1 -gt EXP2
     true if EXP1 is numerically greater than EXP2.

EXP1 -le EXP2
     true if EXP1 is numerically less than or equal to EXP2.

EXP1 -ge EXP2
     true if EXP1 is numerically greater than or equal to EXP2.

( EXP )
     true if EXP is true.

! EXP
     true if EXP is false.

EXP1 && EXP2
     true if EXP1 and EXP2 are both true.

EXP1 || EXP2
     true if either EXP1 or EXP2 is true.


For compatibility, if there is a single argument that is not
syntactically significant, typically a variable, the condition is
treated as a test for whether the expression expands as a string of
non-zero length.  In other words, [[ $var ]] is the same as [[ -n $var
]].  It is recommended that the second, explicit, form be used where
possible.

Normal shell expansion is performed on the FILE, STRING and PATTERN
arguments, but the result of each expansion is constrained to be a
single word, similar to the effect of double quotes.

Filename generation is not performed on any form of argument to
conditions.  However, it can be forced in any case where normal shell
expansion is valid and when the option EXTENDED_GLOB is in effect by
using an explicit glob qualifier of the form (#q) at the end of the
string.  A normal glob qualifier expression may appear between the `q'
and the closing parenthesis; if none appears the expression has no
effect beyond causing filename generation.  The results of filename
generation are joined together to form a single word, as with the
results of other forms of expansion.

This special use of filename generation is only available with the [[
syntax.  If the condition occurs within the [ or test builtin commands
then globbing occurs instead as part of normal command line expansion
before the condition is evaluated.  In this case it may generate
multiple words which are likely to confuse the syntax of the test
command.

For example,


     [[ -n file*(#qN) ]]

produces status zero if and only if there is at least one file in the
current directory beginning with the string `file'.  The globbing
qualifier N ensures that the expression is empty if there is no
matching file.

Pattern metacharacters are active for the PATTERN arguments; the
patterns are the same as those used for filename generation, see *Note
Filename Generation::, but there is no special behaviour of `/' nor
initial dots, and no glob qualifiers are allowed.

In each of the above expressions, if FILE is of the form `/dev/fd/N',
where N is an integer, then the test applied to the open file whose
descriptor number is N, even if the underlying system does not support
the /dev/fd directory.

In the forms which do numeric comparison, the expressions EXP undergo
arithmetic expansion as if they were enclosed in $((...)).

For example, the following:


     [[ ( -f foo || -f bar ) && $report = y* ]] && print File exists.

tests if either file foo or file bar exists, and if so, if the value of
the parameter report begins with `y'; if the complete condition is
true, the message `File exists.' is printed.


File: zsh.info,  Node: Prompt Expansion,  Next: Expansion,  Prev: Conditional Expressions,  Up: Top

13 Prompt Expansion
*******************



13.1 Expansion of Prompt Sequences
==================================

Prompt sequences undergo a special form of expansion.  This type of
expansion is also available using the -P option to the print builtin.

If the PROMPT_SUBST option is set, the prompt string is first subjected
to _parameter expansion_, _command substitution_ and _arithmetic
expansion_.  See *Note Expansion::.

Certain escape sequences may be recognised in the prompt string.

If the PROMPT_BANG option is set, a `!' in the prompt is replaced by
the current history event number.  A literal `!' may then be
represented as `!!'.

If the PROMPT_PERCENT option is set, certain escape sequences that
start with `%' are expanded.  Many escapes are followed by a single
character, although some of these take an optional integer argument that
should appear between the `%' and the next character of the sequence.
More complicated escape sequences are available to provide conditional
expansion.



13.2 Simple Prompt Escapes
==========================



13.2.1 Special characters
-------------------------


%%
     A `%'.

%)
     A `)'.



13.2.2 Login information
------------------------


%l
     The line (tty) the user is logged in on, without `/dev/' prefix.
     If the name starts with `/dev/tty', that prefix is stripped.

%M
     The full machine hostname.

%m
     The hostname up to the first `.'.  An integer may follow the `%'
     to specify how many components of the hostname are desired.  With
     a negative integer, trailing components of the hostname are shown.

%n
     $USERNAME.

%y
     The line (tty) the user is logged in on, without `/dev/' prefix.
     This does not treat `/dev/tty' names specially.



13.2.3 Shell state
------------------


%#
     A `#' if the shell is running with privileges, a `%' if not.
     Equivalent to `%(!.#.%%)'.  The definition of `privileged', for
     these purposes, is that either the effective user ID is zero, or,
     if POSIX.1e capabilities are supported, that at least one
     capability is raised in either the Effective or Inheritable
     capability vectors.

%?
     The return status of the last command executed just before the
     prompt.

%_
     The status of the parser, i.e. the shell constructs (like `if' and
     `for') that have been started on the command line. If given an
     integer number that many strings will be printed; zero or negative
     or no integer means print as many as there are.  This is most
     useful in prompts PS2 for continuation lines and PS4 for debugging
     with the XTRACE option; in the latter case it will also work
     non-interactively.

%^
     The status of the parser in reverse. This is the same as `%_'
     other than the order of strings.  It is often used in RPS2.

%d
%/
     Current working directory.  If an integer follows the `%', it
     specifies a number of trailing components of the current working
     directory to show; zero means the whole path.  A negative integer
     specifies leading components, i.e. %-1d specifies the first
     component.

%~
     As %d and %/, but if the current working directory starts with
     $HOME, that part is replaced by a `~'. Furthermore, if it has a
     named directory as its prefix, that part is replaced by a `~'
     followed by the name of the directory, but only if the result is
     shorter than the full path; *Note Filename Expansion::.

%e
     Evaluation depth of the current sourced file, shell function, or
     eval.  This is incremented or decremented every time the value of
     %N is set or reverted to a previous value, respectively.  This is
     most useful for debugging as part of $PS4.

%h
%!
     Current history event number.

%i
     The line number currently being executed in the script, sourced
     file, or shell function given by %N.  This is most useful for
     debugging as part of $PS4.

%I
     The line number currently being executed in the file %x.  This is
     similar to %i, but the line number is always a line number in the
     file where the code was defined, even if the code is a shell
     function.

%j
     The number of jobs.

%L
     The current value of $SHLVL.

%N
     The name of the script, sourced file, or shell function that zsh is
     currently executing, whichever was started most recently.  If
     there is none, this is equivalent to the parameter $0.  An integer
     may follow the `%' to specify a number of trailing path components
     to show; zero means the full path.  A negative integer specifies
     leading components.

%x
     The name of the file containing the source code currently being
     executed.  This behaves as %N except that function and eval command
     names are not shown, instead the file where they were defined.

%c
%.
%C
     Trailing component of the current working directory.  An integer
     may follow the `%' to get more than one component.  Unless `%C' is
     used, tilde contraction is performed first.  These are deprecated
     as %c and %C are equivalent to %1~ and %1/, respectively, while
     explicit positive integers have the same effect as for the latter
     two sequences.



13.2.4 Date and time
--------------------


%D
     The date in YY-MM-DD format.

%T
     Current time of day, in 24-hour format.

%t
%@
     Current time of day, in 12-hour, am/pm format.

%*
     Current time of day in 24-hour format, with seconds.

%w
     The date in DAY-DD format.

%W
     The date in MM/DD/YY format.

%D{STRING}
     STRING is formatted using the strftime function.  See strftime(3)
     for more details.  Various zsh extensions provide numbers with no
     leading zero or space if the number is a single digit:


    %f
          a day of the month

    %K
          the hour of the day on the 24-hour clock

    %L
          the hour of the day on the 12-hour clock

     In addition, if the system supports the POSIX gettimeofday system
     call, %. provides decimal fractions of a second since the epoch
     with leading zeroes.  By default three decimal places are
     provided, but a number of digits up to 9 may be given following
     the %; hence %6.  outputs microseconds, and %9. outputs
     nanoseconds.  (The latter requires a nanosecond-precision
     clock_gettime; systems lacking this will return a value multiplied
     by the appropriate power of 10.)  A typical example of this is the
     format `%D{%H:%M:%S.%.}'.

     The GNU extension %N is handled as a synonym for %9..

     Additionally, the GNU extension that a `-' between the % and the
     format character causes a leading zero or space to be stripped is
     handled directly by the shell for the format characters d, f, H,
     k, l, m, M, S and y; any other format characters are provided to
     the system's strftime(3) with any leading `-' present, so the
     handling is system dependent.  Further GNU (or other) extensions
     are also passed to strftime(3) and may work if the system supports
     them.



13.2.5 Visual effects
---------------------


%B (%b)
     Start (stop) boldface mode.

%E
     Clear to end of line.

%U (%u)
     Start (stop) underline mode.

%S (%s)
     Start (stop) standout mode.

%F (%f)
     Start (stop) using a different foreground colour, if supported by
     the terminal.  The colour may be specified two ways: either as a
     numeric argument, as normal, or by a sequence in braces following
     the %F, for example %F{red}.  In the latter case the values
     allowed are as described for the fg zle_highlight attribute; *Note
     Character Highlighting::.  This means that numeric colours are
     allowed in the second format also.

%K (%k)
     Start (stop) using a different bacKground colour.  The syntax is
     identical to that for %F and %f.

%{...%}
     Include a string as a literal escape sequence.  The string within
     the braces should not change the cursor position.  Brace pairs can
     nest.

     A positive numeric argument between the % and the { is treated as
     described for %G below.

%G
     Within a %{...%} sequence, include a `glitch': that is, assume
     that a single character width will be output.  This is useful when
     outputting characters that otherwise cannot be correctly handled
     by the shell, such as the alternate character set on some
     terminals.  The characters in question can be included within a
     %{...%} sequence together with the appropriate number of %G
     sequences to indicate the correct width.  An integer between the
     `%' and `G' indicates a character width other than one.  Hence
     %{SEQ%2G%} outputs SEQ and assumes it takes up the width of two
     standard characters.

     Multiple uses of %G accumulate in the obvious fashion; the position
     of the %G is unimportant.  Negative integers are not handled.

     Note that when prompt truncation is in use it is advisable to
     divide up output into single characters within each %{...%} group
     so that the correct truncation point can be found.



13.3 Conditional Substrings in Prompts
======================================


%v
     The value of the first element of the psvar array parameter.
     Following the `%' with an integer gives that element of the array.
     Negative integers count from the end of the array.

%(X.TRUE-TEXT.FALSE-TEXT)
     Specifies a ternary expression.  The character following the X is
     arbitrary; the same character is used to separate the text for the
     `true' result from that for the `false' result.  This separator
     may not appear in the TRUE-TEXT, except as part of a %-escape
     sequence.  A `)' may appear in the FALSE-TEXT as `%)'.  TRUE-TEXT
     and FALSE-TEXT may both contain arbitrarily-nested escape
     sequences, including further ternary expressions.

     The left parenthesis may be preceded or followed by a positive
     integer N, which defaults to zero.  A negative integer will be
     multiplied by -1, except as noted below for `l'.  The test
     character X may be any of the following:


    !
          True if the shell is running with privileges.

    #
          True if the effective uid of the current process is N.

    ?
          True if the exit status of the last command was N.

    _
          True if at least N shell constructs were started.

    C
    /
          True if the current absolute path has at least N elements
          relative to the root directory, hence / is counted as 0
          elements.

    c
    .
    ~
          True if the current path, with prefix replacement, has at
          least N elements relative to the root directory, hence / is
          counted as 0 elements.

    D
          True if the month is equal to N (January = 0).

    d
          True if the day of the month is equal to N.

    e
          True if the evaluation depth is at least N.

    g
          True if the effective gid of the current process is N.

    j
          True if the number of jobs is at least N.

    L
          True if the SHLVL parameter is at least N.

    l
          True if at least N characters have already been printed on
          the current line.  When N is negative, true if at least
          abs(N) characters remain before the opposite margin (thus the
          left margin for RPROMPT).

    S
          True if the SECONDS parameter is at least N.

    T
          True if the time in hours is equal to N.

    t
          True if the time in minutes is equal to N.

    v
          True if the array psvar has at least N elements.

    V
          True if element N of the array psvar is set and non-empty.

    w
          True if the day of the week is equal to N (Sunday = 0).

%<STRING<
%>STRING>
%[XSTRING]
     Specifies truncation behaviour for the remainder of the prompt
     string.  The third, deprecated, form is equivalent to `%XSTRINGX',
     i.e. X may be `<' or `>'.  The STRING will be displayed in place
     of the truncated portion of any string; note this does not undergo
     prompt expansion.

     The numeric argument, which in the third form may appear
     immediately after the `[', specifies the maximum permitted length
     of the various strings that can be displayed in the prompt.  In
     the first two forms, this numeric argument may be negative, in
     which case the truncation length is determined by subtracting the
     absolute value of the numeric argument from the number of
     character positions remaining on the current prompt line.  If this
     results in a zero or negative length, a length of 1 is used.  In
     other words, a negative argument arranges that after truncation at
     least N characters remain before the right margin (left margin for
     RPROMPT).

     The forms with `<' truncate at the left of the string, and the
     forms with `>' truncate at the right of the string.  For example,
     if the current directory is `/home/pike', the prompt `%8<..<%/'
     will expand to `..e/pike'.  In this string, the terminating
     character (`<', `>' or `]'), or in fact any character, may be
     quoted by a preceding `\'; note when using print -P, however, that
     this must be doubled as the string is also subject to standard
     print processing, in addition to any backslashes removed by a
     double quoted string:  the worst case is therefore `print -P
     "%<\\\\<<..."'.

     If the STRING is longer than the specified truncation length, it
     will appear in full, completely replacing the truncated string.

     The part of the prompt string to be truncated runs to the end of
     the string, or to the end of the next enclosing group of the `%('
     construct, or to the next truncation encountered at the same
     grouping level (i.e. truncations inside a `%(' are separate), which
     ever comes first.  In particular, a truncation with argument zero
     (e.g., `%<<') marks the end of the range of the string to be
     truncated while turning off truncation from there on. For example,
     the prompt `%10<...<%~%<<%# ' will print a truncated
     representation of the current directory, followed by a `%' or `#',
     followed by a space.  Without the `%<<', those two characters
     would be included in the string to be truncated.  Note that
     `%-0<<' is not equivalent to `%<<' but specifies that the prompt
     is truncated at the right margin.

     Truncation applies only within each individual line of the prompt,
     as delimited by embedded newlines (if any).  If the total length
     of any line of the prompt after truncation is greater than the
     terminal width, or if the part to be truncated contains embedded
     newlines, truncation behavior is undefined and may change in a
     future version of the shell.  Use `%-N(l.TRUE-TEXT.FALSE-TEXT)' to
     remove parts of the prompt when the available space is less than N.



File: zsh.info,  Node: Expansion,  Next: Parameters,  Prev: Prompt Expansion,  Up: Top

14 Expansion
************

The following types of expansions are performed in the indicated order
in five steps:


_History Expansion_
     This is performed only in interactive shells.

_Alias Expansion_
     Aliases are expanded immediately before the command line is parsed
     as explained in *Note Aliasing::.

_Process Substitution_
_Parameter Expansion_
_Command Substitution_
_Arithmetic Expansion_
_Brace Expansion_
     These five are performed in left-to-right fashion.  On each
     argument, any of the five steps that are needed are performed one
     after the other.  Hence, for example, all the parts of parameter
     expansion are completed before command substitution is started.
     After these expansions, all unquoted occurrences of the characters
     `\',`'' and `"' are removed.

_Filename Expansion_
     If the SH_FILE_EXPANSION option is set, the order of expansion is
     modified for compatibility with `sh' and `ksh'.  In that case
     _filename expansion_ is performed immediately after _alias
     expansion_, preceding the set of five expansions mentioned above.

_Filename Generation_
     This expansion, commonly referred to as `globbing', is always done
     last.


The following sections explain the types of expansion in detail.



* Menu:

* History Expansion::
* Process Substitution::
* Parameter Expansion::
* Command Substitution::
* Arithmetic Expansion::
* Brace Expansion::
* Filename Expansion::
* Filename Generation::


File: zsh.info,  Node: History Expansion,  Next: Process Substitution,  Up: Expansion

14.1 History Expansion
======================

History expansion allows you to use words from previous command lines
in the command line you are typing.  This simplifies spelling
corrections and the repetition of complicated commands or arguments.

Immediately before execution, each command is saved in the history list,
the size of which is controlled by the HISTSIZE parameter.  The one
most recent command is always retained in any case.  Each saved command
in the history list is called a history _event_ and is assigned a
number, beginning with 1 (one) when the shell starts up.  The history
number that you may see in your prompt (see *Note Prompt Expansion::)
is the number that is to be assigned to the _next_ command.



* Menu:

* Overview::
* Event Designators::
* Word Designators::
* Modifiers::


File: zsh.info,  Node: Overview,  Next: Event Designators,  Up: History Expansion

14.1.1 Overview
---------------

A history expansion begins with the first character of the histchars
parameter, which is `!' by default, and may occur anywhere on the
command line, including inside double quotes (but not inside single
quotes '...' or C-style quotes $'...' nor when escaped with a
backslash).

The first character is followed by an optional event designator (*Note
Event Designators::) and then an optional word designator (*Note Word
Designators::); if neither of these designators is present, no history
expansion occurs.

Input lines containing history expansions are echoed after being
expanded, but before any other expansions take place and before the
command is executed.  It is this expanded form that is recorded as the
history event for later references.

History expansions do not nest.

By default, a history reference with no event designator refers to the
same event as any preceding history reference on that command line; if
it is the only history reference in a command, it refers to the previous
command.  However, if the option CSH_JUNKIE_HISTORY is set, then every
history reference with no event specification _always_ refers to the
previous command.

For example, `!' is the event designator for the previous command, so
`!!:1' always refers to the first word of the previous command, and
`!!$' always refers to the last word of the previous command.  With
CSH_JUNKIE_HISTORY set, then `!:1' and `!$' function in the same manner
as `!!:1' and `!!$', respectively.  Conversely, if CSH_JUNKIE_HISTORY
is unset, then `!:1' and `!$' refer to the first and last words,
respectively, of the same event referenced by the nearest other history
reference preceding them on the current command line, or to the
previous command if there is no preceding reference.

The character sequence `^FOO^BAR' (where `^' is actually the second
character of the histchars parameter) repeats the last command,
replacing the string FOO with BAR.  More precisely, the sequence
`^FOO^BAR^' is synonymous with `!!:s^FOO^BAR^', hence other modifiers
(see *Note Modifiers::) may follow the final `^'.  In particular,
`^FOO^BAR^:G' performs a global substitution.

If the shell encounters the character sequence `!"'  in the input, the
history mechanism is temporarily disabled until the current list (see
*Note Shell Grammar::) is fully parsed.  The `!"' is removed from the
input, and any subsequent `!' characters have no special significance.

A less convenient but more comprehensible form of command history
support is provided by the fc builtin.


File: zsh.info,  Node: Event Designators,  Next: Word Designators,  Prev: Overview,  Up: History Expansion

14.1.2 Event Designators
------------------------

An event designator is a reference to a command-line entry in the
history list.  In the list below, remember that the initial `!' in each
item may be changed to another character by setting the histchars
parameter.


!
     Start a history expansion, except when followed by a blank,
     newline, `=' or `('.  If followed immediately by a word designator
     (*Note Word Designators::), this forms a history reference with no
     event designator (*Note Overview::).

!!
     Refer to the previous command.  By itself, this expansion repeats
     the previous command.

!N
     Refer to command-line N.

!-N
     Refer to the current command-line minus N.

!STR
     Refer to the most recent command starting with STR.

!?STR[?]
     Refer to the most recent command containing STR.  The trailing `?'
     is necessary if this reference is to be followed by a modifier or
     followed by any text that is not to be considered part of STR.

!#
     Refer to the current command line typed in so far.  The line is
     treated as if it were complete up to and including the word before
     the one with the `!#' reference.

!{...}
     Insulate a history reference from adjacent characters (if
     necessary).



File: zsh.info,  Node: Word Designators,  Next: Modifiers,  Prev: Event Designators,  Up: History Expansion

14.1.3 Word Designators
-----------------------

A word designator indicates which word or words of a given command line
are to be included in a history reference.  A `:' usually separates the
event specification from the word designator.  It may be omitted only
if the word designator begins with a `^', `$', `*', `-' or `%'.  Word
designators include:


0
     The first input word (command).

N
     The Nth argument.

^
     The first argument.  That is, 1.

$
     The last argument.

%
     The word matched by (the most recent) ?STR search.

X-Y
     A range of words; X defaults to 0.

*
     All the arguments, or a null value if there are none.

X*
     Abbreviates `X-$'.

X-
     Like `X*' but omitting word $.

Note that a `%' word designator works only when used in one of `!%',
`!:%' or `!?STR?:%', and only when used after a !? expansion (possibly
in an earlier command).  Anything else results in an error, although
the error may not be the most obvious one.


File: zsh.info,  Node: Modifiers,  Prev: Word Designators,  Up: History Expansion

14.1.4 Modifiers
----------------

After the optional word designator, you can add a sequence of one or
more of the following modifiers, each preceded by a `:'.  These
modifiers also work on the result of _filename generation_ and
_parameter expansion_, except where noted.


a
     Turn a file name into an absolute path:  prepends the current
     directory, if necessary; remove `.' path segments; and remove `..'
     path segments and the segments that immediately precede them.

     This transformation is agnostic about what is in the filesystem,
     i.e. is on the logical, not the physical directory.  It takes
     place in the same manner as when changing directories when neither
     of the options CHASE_DOTS or CHASE_LINKS is set.  For example,
     `/before/here/../after' is always transformed to `/before/after',
     regardless of whether `/before/here' exists or what kind of object
     (dir, file, symlink, etc.) it is.

A
     Turn a file name into an absolute path as the `a' modifier does,
     and _then_ pass the result through the realpath(3) library
     function to resolve symbolic links.

     Note: on systems that do not have a realpath(3) library function,
     symbolic links are not resolved, so on those systems `a' and `A'
     are equivalent.

     Note: foo:A and realpath(foo) are different on some inputs.  For
     realpath(foo) semantics, see the `P` modifier.

c
     Resolve a command name into an absolute path by searching the
     command path given by the PATH variable.  This does not work for
     commands containing directory parts.  Note also that this does not
     usually work as a glob qualifier unless a file of the same name is
     found in the current directory.

e
     Remove all but the part of the filename extension following the
     `.'; see the definition of the filename extension in the
     description of the r modifier below.  Note that according to that
     definition the result will be empty if the string ends with a `.'.

h [ DIGITS ]
     Remove a trailing pathname component, shortening the path by one
     directory level: this is the `head' of the pathname.  This works
     like `dirname'.  If the h is followed immediately (with no spaces
     or other separator) by any number of decimal digits, and the value
     of the resulting number is non-zero, that number of leading
     components is preserved instead of the final component being
     removed.  In an absolute path the leading `/' is the first
     component, so, for example, if var=/my/path/to/something, then
     ${var:h3} substitutes /my/path.  Consecutive `/'s are treated the
     same as a single `/'.  In parameter substitution, digits may only
     be used if the expression is in braces, so for example the short
     form substitution $var:h2 is treated as ${var:h}2, not as
     ${var:h2}.  No restriction applies to the use of digits in history
     substitution or globbing qualifiers.  If more components are
     requested than are present, the entire path is substituted (so
     this does not trigger a `failed modifier' error in history
     expansion).

l
     Convert the words to all lowercase.

p
     Print the new command but do not execute it.  Only works with
     history expansion.

P
     Turn a file name into an absolute path, like realpath(3).  The
     resulting path will be absolute, will refer to the same directory
     entry as the input filename, and none of its components will be
     symbolic links or equal to `.' or `..'.

     Unlike realpath(3), non-existent trailing components are permitted
     and preserved.

q
     Quote the substituted words, escaping further substitutions.  Works
     with history expansion and parameter expansion, though for
     parameters it is only useful if the resulting text is to be
     re-evaluated such as by eval.

Q
     Remove one level of quotes from the substituted words.

r
     Remove a filename extension leaving the root name.  Strings with no
     filename extension are not altered.  A filename extension is a `.'
     followed by any number of characters (including zero) that are
     neither `.' nor `/' and that continue to the end of the string.
     For example, the extension of `foo.orig.c' is `.c', and
     `dir.c/foo' has no extension.

s/L/R[/]
     Substitute R for L as described below.  The substitution is done
     only for the first string that matches L.  For arrays and for
     filename generation, this applies to each word of the expanded
     text.  See below for further notes on substitutions.

     The forms `gs/L/R' and `s/L/R/:G' perform global substitution,
     i.e. substitute every occurrence of R for L.  Note that the g or
     :G must appear in exactly the position shown.

     See further notes on this form of substitution below.

&
     Repeat the previous s substitution.  Like s, may be preceded
     immediately by a g.  In parameter expansion the & must appear
     inside braces, and in filename generation it must be quoted with a
     backslash.

t [ DIGITS ]
     Remove all leading pathname components, leaving the final
     component (tail).  This works like `basename'.  Any trailing
     slashes are first removed.  Decimal digits are handled as
     described above for (h), but in this case that number of trailing
     components is preserved instead of the default 1; 0 is treated the
     same as 1.

u
     Convert the words to all uppercase.

x
     Like q, but break into words at whitespace.  Does not work with
     parameter expansion.


The s/L/R/ substitution works as follows.  By default the left-hand
side of substitutions are not patterns, but character strings.  Any
character can be used as the delimiter in place of `/'.  A backslash
quotes the delimiter character.  The character `&', in the
right-hand-side R, is replaced by the text from the left-hand-side L.
The `&' can be quoted with a backslash.  A null L uses the previous
string either from the previous L or from the contextual scan string S
from `!?S'.  You can omit the rightmost delimiter if a newline
immediately follows R; the rightmost `?' in a context scan can
similarly be omitted.  Note the same record of the last L and R is
maintained across all forms of expansion.

Note that if a `&' is used within glob qualifiers an extra backslash is
needed as a & is a special character in this case.

Also note that the order of expansions affects the interpretation of L
and R.  When used in a history expansion, which occurs before any other
expansions, L and R are treated as literal strings (except as explained
for HIST_SUBST_PATTERN below).  When used in parameter expansion, the
replacement of R into the parameter's value is done first, and then any
additional process, parameter, command, arithmetic, or brace references
are applied, which may evaluate those substitutions and expansions more
than once if L appears more than once in the starting value.  When used
in a glob qualifier, any substitutions or expansions are performed once
at the time the qualifier is parsed, even before the `:s' expression
itself is divided into L and R sides.

If the option HIST_SUBST_PATTERN is set, L is treated as a pattern of
the usual form described in *Note Filename Generation::.  This can be
used in all the places where modifiers are available; note, however,
that in globbing qualifiers parameter substitution has already taken
place, so parameters in the replacement string should be quoted to
ensure they are replaced at the correct time.  Note also that
complicated patterns used in globbing qualifiers may need the extended
glob qualifier notation (#q:s/.../.../) in order for the shell to
recognize the expression as a glob qualifier.  Further, note that bad
patterns in the substitution are not subject to the NO_BAD_PATTERN
option so will cause an error.

When HIST_SUBST_PATTERN is set, L may start with a # to indicate that
the pattern must match at the start of the string to be substituted,
and a % may appear at the start or after an # to indicate that the
pattern must match at the end of the string to be substituted.  The %
or # may be quoted with two backslashes.

For example, the following piece of filename generation code with the
EXTENDED_GLOB option:


     print -r -- *.c(#q:s/#%(#b)s(*).c/'S${match[1]}.C'/)

takes the expansion of *.c and applies the glob qualifiers in the
(#q...) expression, which consists of a substitution modifier anchored
to the start and end of each word (#%).  This turns on backreferences
((#b)), so that the parenthesised subexpression is available in the
replacement string as ${match[1]}.  The replacement string is quoted so
that the parameter is not substituted before the start of filename
generation.

The following f, F, w and W modifiers work only with parameter
expansion and filename generation.  They are listed here to provide a
single point of reference for all modifiers.


f
     Repeats the immediately (without a colon) following modifier until
     the resulting word doesn't change any more.

F:EXPR:
     Like f, but repeats only N times if the expression EXPR evaluates
     to N.  Any character can be used instead of the `:'; if `(', `[',
     or `{' is used as the opening delimiter, the closing delimiter
     should be ')', `]', or `}', respectively.

w
     Makes the immediately following modifier work on each word in the
     string.

W:SEP:
     Like w but words are considered to be the parts of the string that
     are separated by SEP. Any character can be used instead of the
     `:'; opening parentheses are handled specially, see above.



File: zsh.info,  Node: Process Substitution,  Next: Parameter Expansion,  Prev: History Expansion,  Up: Expansion

14.2 Process Substitution
=========================

Each part of a command argument that takes the form `<(LIST)',
`>(LIST)' or `=(LIST)' is subject to process substitution.  The
expression may be preceded or followed by other strings except that, to
prevent clashes with commonly occurring strings and patterns, the last
form must occur at the start of a command argument, and the forms are
only expanded when first parsing command or assignment arguments.
Process substitutions may be used following redirection operators; in
this case, the substitution must appear with no trailing string.

Note that `<<(LIST)' is not a special syntax; it is equivalent to `<
<(LIST)', redirecting standard input from the result of process
substitution.  Hence all the following documentation applies.  The
second form (with the space) is recommended for clarity.

In the case of the < or > forms, the shell runs the commands in LIST as
a subprocess of the job executing the shell command line.  If the
system supports the /dev/fd mechanism, the command argument is the name
of the device file corresponding to a file descriptor; otherwise, if
the system supports named pipes (FIFOs), the command argument will be a
named pipe.  If the form with > is selected then writing on this
special file will provide input for LIST.  If < is used, then the file
passed as an argument will be connected to the output of the LIST
process.  For example,


     paste <(cut -f1 FILE1) <(cut -f3 FILE2) |
     tee >(PROCESS1) >(PROCESS2) >/dev/null

cuts fields 1 and 3 from the files FILE1 and FILE2 respectively, pastes
the results together, and sends it to the processes PROCESS1 and
PROCESS2.

If =(...) is used instead of <(...), then the file passed as an
argument will be the name of a temporary file containing the output of
the LIST process.  This may be used instead of the < form for a program
that expects to lseek (see lseek(2)) on the input file.

There is an optimisation for substitutions of the form =(<<<ARG), where
ARG is a single-word argument to the here-string redirection <<<.  This
form produces a file name containing the value of ARG after any
substitutions have been performed.  This is handled entirely within the
current shell.  This is effectively the reverse of the special form
$(<ARG) which treats ARG as a file name and replaces it with the file's
contents.

The = form is useful as both the /dev/fd and the named pipe
implementation of <(...) have drawbacks.  In the former case, some
programmes may automatically close the file descriptor in question
before examining the file on the command line, particularly if this is
necessary for security reasons such as when the programme is running
setuid.  In the second case, if the programme does not actually open
the file, the subshell attempting to read from or write to the pipe
will (in a typical implementation, different operating systems may have
different behaviour) block for ever and have to be killed explicitly.
In both cases, the shell actually supplies the information using a
pipe, so that programmes that expect to lseek (see lseek(2)) on the
file will not work.

Also note that the previous example can be more compactly and
efficiently written (provided the MULTIOS option is set) as:


     paste <(cut -f1 FILE1) <(cut -f3 FILE2) > >(PROCESS1) > >(PROCESS2)

The shell uses pipes instead of FIFOs to implement the latter two
process substitutions in the above example.

There is an additional problem with >(PROCESS); when this is attached
to an external command, the parent shell does not wait for PROCESS to
finish and hence an immediately following command cannot rely on the
results being complete.  The problem and solution are the same as
described in the section _MULTIOS_ in *Note Redirection::.  Hence in a
simplified version of the example above:


     paste <(cut -f1 FILE1) <(cut -f3 FILE2) > >(PROCESS)

(note that no MULTIOS are involved), PROCESS will be run asynchronously
as far as the parent shell is concerned.  The workaround is:


     { paste <(cut -f1 FILE1) <(cut -f3 FILE2) } > >(PROCESS)

The extra processes here are spawned from the parent shell which will
wait for their completion.

Another problem arises any time a job with a substitution that requires
a temporary file is disowned by the shell, including the case where
`&!' or `&|' appears at the end of a command containing a substitution.
In that case the temporary file will not be cleaned up as the shell no
longer has any memory of the job.  A workaround is to use a subshell,
for example,


     (mycmd =(myoutput)) &!

as the forked subshell will wait for the command to finish then remove
the temporary file.

A general workaround to ensure a process substitution endures for an
appropriate length of time is to pass it as a parameter to an anonymous
shell function (a piece of shell code that is run immediately with
function scope).  For example, this code:


     () {
        print File $1:
        cat $1
     } =(print This be the verse)

outputs something resembling the following


     File /tmp/zsh6nU0kS:
     This be the verse

The temporary file created by the process substitution will be deleted
when the function exits.




File: zsh.info,  Node: Parameter Expansion,  Next: Command Substitution,  Prev: Process Substitution,  Up: Expansion

14.3 Parameter Expansion
========================

The character `$' is used to introduce parameter expansions.  See *Note
Parameters:: for a description of parameters, including arrays,
associative arrays, and subscript notation to access individual array
elements.

Note in particular the fact that words of unquoted parameters are not
automatically split on whitespace unless the option SH_WORD_SPLIT is
set; see references to this option below for more details.  This is an
important difference from other shells.  However, as in other shells,
null words are elided from unquoted parameters' expansions.

With default options, after the assignments:


     array=("first word" "" "third word")
     scalar="only word"

then $array substitutes two words, `first word' and `third word', and
$scalar substitutes a single word `only word'.  Note that second
element of array was elided.  Scalar parameters can be elided too if
their value is null (empty).  To avoid elision, use quoting as follows:
"$scalar" for scalars and "${array[@]}" or "${(@)array}" for arrays.
(The last two forms are equivalent.)

Parameter expansions can involve _flags_, as in `${(@kv)aliases}', and
other operators, such as `${PREFIX:-"/usr/local"}'.  Parameter
expansions can also be nested.  These topics will be introduced below.
The full rules are complicated and are noted at the end.

In the expansions discussed below that require a pattern, the form of
the pattern is the same as that used for filename generation; see *Note
Filename Generation::.  Note that these patterns, along with the
replacement text of any substitutions, are themselves subject to
parameter expansion, command substitution, and arithmetic expansion.
In addition to the following operations, the colon modifiers described
in *Note Modifiers:: in *Note History Expansion:: can be applied:  for
example, ${i:s/foo/bar/} performs string substitution on the expansion
of parameter $i.

In the following descriptions, `WORD' refers to a single word
substituted on the command line, not necessarily a space delimited word.


${NAME}
     The value, if any, of the parameter NAME is substituted.  The
     braces are required if the expansion is to be followed by a
     letter, digit, or underscore that is not to be interpreted as part
     of NAME.  In addition, more complicated forms of substitution
     usually require the braces to be present; exceptions, which only
     apply if the option KSH_ARRAYS is not set, are a single subscript
     or any colon modifiers appearing after the name, or any of the
     characters `^', `=', `~', `#' or `+' appearing before the name,
     all of which work with or without braces.

     If NAME is an array parameter, and the KSH_ARRAYS option is not
     set, then the value of each element of NAME is substituted, one
     element per word.  Otherwise, the expansion results in one word
     only; with KSH_ARRAYS, this is the first element of an array.  No
     field splitting is done on the result unless the SH_WORD_SPLIT
     option is set.  See also the flags = and s:STRING:.

${+NAME}
     If NAME is the name of a set parameter `1' is substituted,
     otherwise `0' is substituted.

${NAME-WORD}
${NAME:-WORD}
     If NAME is set, or in the second form is non-null, then substitute
     its value; otherwise substitute WORD.  In the second form NAME may
     be omitted, in which case WORD is always substituted.

${NAME+WORD}
${NAME:+WORD}
     If NAME is set, or in the second form is non-null, then substitute
     WORD; otherwise substitute nothing.

${NAME=WORD}
${NAME:=WORD}
${NAME::=WORD}
     In the first form, if NAME is unset then set it to WORD; in the
     second form, if NAME is unset or null then set it to WORD; and in
     the third form, unconditionally set NAME to WORD.  In all forms,
     the value of the parameter is then substituted.

${NAME?WORD}
${NAME:?WORD}
     In the first form, if NAME is set, or in the second form if NAME
     is both set and non-null, then substitute its value; otherwise,
     print WORD and exit from the shell.  Interactive shells instead
     return to the prompt.  If WORD is omitted, then a standard message
     is printed.  Note that WORD is expanded even though its value is
     not substituted onto the command line.


In any of the above expressions that test a variable and substitute an
alternate WORD, note that you can use standard shell quoting in the
WORD value to selectively override the splitting done by the
SH_WORD_SPLIT option and the = flag, but not splitting by the s:STRING:
flag.

In the following expressions, when NAME is an array and the
substitution is not quoted, or if the `(@)' flag or the NAME[@] syntax
is used, matching and replacement is performed on each array element
separately.


${NAME#PATTERN}
${NAME##PATTERN}
     If the PATTERN matches the beginning of the value of NAME, then
     substitute the value of NAME with the matched portion deleted;
     otherwise, just substitute the value of NAME.  In the first form,
     the smallest matching pattern is preferred; in the second form,
     the largest matching pattern is preferred.

${NAME%PATTERN}
${NAME%%PATTERN}
     If the PATTERN matches the end of the value of NAME, then
     substitute the value of NAME with the matched portion deleted;
     otherwise, just substitute the value of NAME.  In the first form,
     the smallest matching pattern is preferred; in the second form,
     the largest matching pattern is preferred.

${NAME:#PATTERN}
     If the PATTERN matches the value of NAME, then substitute the
     empty string; otherwise, just substitute the value of NAME.  If
     NAME is an array the matching array elements are removed (use the
     `(M)' flag to remove the non-matched elements).

${NAME:|ARRAYNAME}
     If ARRAYNAME is the name (N.B., not contents) of an array
     variable, then any elements contained in ARRAYNAME are removed
     from the substitution of NAME.  If the substitution is scalar,
     either because NAME is a scalar variable or the expression is
     quoted, the elements of ARRAYNAME are instead tested against the
     entire expression.

${NAME:*ARRAYNAME}
     Similar to the preceding substitution, but in the opposite sense,
     so that entries present in both the original substitution and as
     elements of ARRAYNAME are retained and others removed.

${NAME:^ARRAYNAME}
${NAME:^^ARRAYNAME}
     Zips two arrays, such that the output array is twice as long as the
     shortest (longest for `:^^') of name and arrayname, with the
     elements alternatingly being picked from them. For `:^', if one of
     the input arrays is longer, the output will stop when the end of
     the shorter array is reached.  Thus,


          a=(1 2 3 4); b=(a b); print ${a:^b}

     will output `1 a 2 b'.  For `:^^', then the input is repeated
     until all of the longer array has been used up and the above will
     output `1 a 2 b 3 a 4 b'.

     Either or both inputs may be a scalar, they will be treated as an
     array of length 1 with the scalar as the only element. If either
     array is empty, the other array is output with no extra elements
     inserted.

     Currently the following code will output `a b' and `1' as two
     separate elements, which can be unexpected. The second print
     provides a workaround which should continue to work if this is
     changed.


          a=(a b); b=(1 2); print -l "${a:^b}"; print -l "${${a:^b}}"

${NAME:OFFSET}
${NAME:OFFSET:LENGTH}
     This syntax gives effects similar to parameter subscripting in the
     form $NAME[START,END], but is compatible with other shells; note
     that both OFFSET and LENGTH are interpreted differently from the
     components of a subscript.

     If OFFSET is non-negative, then if the variable NAME is a scalar
     substitute the contents starting OFFSET characters from the first
     character of the string, and if NAME is an array substitute
     elements starting OFFSET elements from the first element.  If
     LENGTH is given, substitute that many characters or elements,
     otherwise the entire rest of the scalar or array.

     A positive OFFSET is always treated as the offset of a character or
     element in NAME from the first character or element of the array
     (this is different from native zsh subscript notation).  Hence 0
     refers to the first character or element regardless of the setting
     of the option KSH_ARRAYS.

     A negative offset counts backwards from the end of the scalar or
     array, so that -1 corresponds to the last character or element,
     and so on.

     When positive, LENGTH counts from the OFFSET position toward the
     end of the scalar or array.  When negative, LENGTH counts back
     from the end.  If this results in a position smaller than OFFSET,
     a diagnostic is printed and nothing is substituted.

     The option MULTIBYTE is obeyed, i.e. the offset and length count
     multibyte characters where appropriate.

     OFFSET and LENGTH undergo the same set of shell substitutions as
     for scalar assignment; in addition, they are then subject to
     arithmetic evaluation.  Hence, for example


          print ${foo:3}
          print ${foo: 1 + 2}
          print ${foo:$(( 1 + 2))}
          print ${foo:$(echo 1 + 2)}

     all have the same effect, extracting the string starting at the
     fourth character of $foo if the substitution would otherwise
     return a scalar, or the array starting at the fourth element if
     $foo would return an array.  Note that with the option KSH_ARRAYS
     $foo always returns a scalar (regardless of the use of the offset
     syntax) and a form such as ${foo[*]:3} is required to extract
     elements of an array named foo.

     If OFFSET is negative, the - may not appear immediately after the
     : as this indicates the ${NAME:-WORD} form of substitution.
     Instead, a space may be inserted before the -.  Furthermore,
     neither OFFSET nor LENGTH may begin with an alphabetic character
     or & as these are used to indicate history-style modifiers.  To
     substitute a value from a variable, the recommended approach is to
     precede it with a $ as this signifies the intention (parameter
     substitution can easily be rendered unreadable); however, as
     arithmetic substitution is performed, the expression ${var: offs}
     does work, retrieving the offset from $offs.

     For further compatibility with other shells there is a special case
     for array offset 0.  This usually accesses the first element of
     the array.  However, if the substitution refers to the positional
     parameter array, e.g. $@ or $*, then offset 0 instead refers to
     $0, offset 1 refers to $1, and so on.  In other words, the
     positional parameter array is effectively extended by prepending
     $0.  Hence ${*:0:1} substitutes $0 and ${*:1:1} substitutes $1.

${NAME/PATTERN/REPL}
${NAME//PATTERN/REPL}
${NAME:/PATTERN/REPL}
     Replace the longest possible match of PATTERN in the expansion of
     parameter NAME by string REPL.  The first form replaces just the
     first occurrence, the second form all occurrences, and the third
     form replaces only if PATTERN matches the entire string.  Both
     PATTERN and REPL are subject to double-quoted substitution, so
     that expressions like ${name/$opat/$npat} will work, but obey the
     usual rule that pattern characters in $opat are not treated
     specially unless either the option GLOB_SUBST is set, or $opat is
     instead substituted as ${~opat}.

     The PATTERN may begin with a `#', in which case the PATTERN must
     match at the start of the string, or `%', in which case it must
     match at the end of the string, or `#%' in which case the PATTERN
     must match the entire string.  The REPL may be an empty string, in
     which case the final `/' may also be omitted.  To quote the final
     `/' in other cases it should be preceded by a single backslash;
     this is not necessary if the `/' occurs inside a substituted
     parameter.  Note also that the `#', `%' and `#% are not active if
     they occur inside a substituted parameter, even at the start.

     If, after quoting rules apply, ${NAME} expands to an array, the
     replacements act on each element individually.  Note also the
     effect of the I and S parameter expansion flags below; however,
     the flags M, R, B, E and N are not useful.

     For example,


          foo="twinkle twinkle little star" sub="t*e" rep="spy"
          print ${foo//${~sub}/$rep}
          print ${(S)foo//${~sub}/$rep}

     Here, the `~' ensures that the text of $sub is treated as a
     pattern rather than a plain string.  In the first case, the longest
     match for t*e is substituted and the result is `spy star', while
     in the second case, the shortest matches are taken and the result
     is `spy spy lispy star'.

${#SPEC}
     If SPEC is one of the above substitutions, substitute the length
     in characters of the result instead of the result itself.  If SPEC
     is an array expression, substitute the number of elements of the
     result.  This has the side-effect that joining is skipped even in
     quoted forms, which may affect other sub-expressions in SPEC.
     Note that `^', `=', and `~', below, must appear to the left of `#'
     when these forms are combined.

     If the option POSIX_IDENTIFIERS is not set, and SPEC is a simple
     name, then the braces are optional; this is true even for special
     parameters so e.g. $#- and $#* take the length of the string $-
     and the array $* respectively.  If POSIX_IDENTIFIERS is set, then
     braces are required for the # to be treated in this fashion.

${^SPEC}
${^^SPEC}
     Turn on the RC_EXPAND_PARAM option for the evaluation of SPEC; if
     the `^' is doubled, turn it off.  When this option is set, array
     expansions of the form FOO${XX}BAR, where the parameter XX is set
     to (A B C), are substituted with `FOOABAR FOOBBAR FOOCBAR' instead
     of the default `FOOA B CBAR'.  Note that an empty array will
     therefore cause all arguments to be removed.

     Internally, each such expansion is converted into the equivalent
     list for brace expansion.  E.g., ${^var} becomes
     {$var[1],$var[2],...}, and is processed as described in *Note
     Brace Expansion:: below: note, however, the expansion happens
     immediately, with any explicit brace expansion happening later.
     If word splitting is also in effect the $var[N] may themselves be
     split into different list elements.

${=SPEC}
${==SPEC}
     Perform word splitting using the rules for SH_WORD_SPLIT during the
     evaluation of SPEC, but regardless of whether the parameter
     appears in double quotes; if the `=' is doubled, turn it off.  This
     forces parameter expansions to be split into separate words before
     substitution, using IFS as a delimiter.  This is done by default
     in most other shells.

     Note that splitting is applied to WORD in the assignment forms of
     SPEC _before_ the assignment to NAME is performed.  This affects
     the result of array assignments with the A flag.

${~SPEC}
${~~SPEC}
     Turn on the GLOB_SUBST option for the evaluation of SPEC; if the
     `~' is doubled, turn it off.  When this option is set, the string
     resulting from the expansion will be interpreted as a pattern
     anywhere that is possible, such as in filename expansion and
     filename generation and pattern-matching contexts like the right
     hand side of the `=' and `!=' operators in conditions.

     In nested substitutions, note that the effect of the ~ applies to
     the result of the current level of substitution.  A surrounding
     pattern operation on the result may cancel it.  Hence, for
     example, if the parameter foo is set to *, ${~foo//\*/*.c} is
     substituted by the pattern *.c, which may be expanded by filename
     generation, but ${${~foo}//\*/*.c} substitutes to the string *.c,
     which will not be further expanded.


If a ${...} type parameter expression or a $(...) type command
substitution is used in place of NAME above, it is expanded first and
the result is used as if it were the value of NAME.  Thus it is
possible to perform nested operations:  ${${foo#head}%tail} substitutes
the value of $foo with both `head' and `tail' deleted.  The form with
$(...) is often useful in combination with the flags described next;
see the examples below.  Each NAME or nested ${...} in a parameter
expansion may also be followed by a subscript expression as described in
*Note Array Parameters::.

Note that double quotes may appear around nested expressions, in which
case only the part inside is treated as quoted; for example,
${(f)"$(foo)"} quotes the result of $(foo), but the flag `(f)' (see
below) is applied using the rules for unquoted expansions.  Note
further that quotes are themselves nested in this context; for example,
in "${(@f)"$(foo)"}", there are two sets of quotes, one surrounding the
whole expression, the other (redundant) surrounding the $(foo) as
before.



14.3.1 Parameter Expansion Flags
--------------------------------

If the opening brace is directly followed by an opening parenthesis,
the string up to the matching closing parenthesis will be taken as a
list of flags.  In cases where repeating a flag is meaningful, the
repetitions need not be consecutive; for example, `(q%q%q)' means the
same thing as the more readable `(%%qqq)'.  The following flags are
supported:


#
     Evaluate the resulting words as numeric expressions and interpret
     these as character codes.  Output the corresponding characters.
     Note that this form is entirely distinct from use of the # without
     parentheses.

     If the MULTIBYTE option is set and the number is greater than 127
     (i.e. not an ASCII character) it is treated as a Unicode character.

%
     Expand all % escapes in the resulting words in the same way as in
     prompts (see *Note Prompt Expansion::). If this flag is given
     twice, full prompt expansion is done on the resulting words,
     depending on the setting of the PROMPT_PERCENT, PROMPT_SUBST and
     PROMPT_BANG options.

@
     In double quotes, array elements are put into separate words.
     E.g., `"${(@)foo}"' is equivalent to `"${foo[@]}"' and
     `"${(@)foo[1,2]}"' is the same as `"$foo[1]" "$foo[2]"'.  This is
     distinct from _field splitting_ by the f, s or z flags, which
     still applies within each array element.

A
     Convert the substitution into an array expression, even if it
     otherwise would be scalar.  This has lower precedence than
     subscripting, so one level of nested expansion is required in
     order that subscripts apply to array elements.  Thus
     ${${(A)NAME}[1]} yields the full value of NAME when NAME is scalar.

     This assigns an array parameter with `${...=...}', `${...:=...}'
     or `${...::=...}'.  If this flag is repeated (as in `AA'), assigns
     an associative array parameter.  Assignment is made before sorting
     or padding; if field splitting is active, the WORD part is split
     before assignment.  The NAME part may be a subscripted range for
     ordinary arrays; when assigning an associative array, the WORD
     part _must_ be converted to an array, for example by using
     `${(AA)=NAME=...}' to activate field splitting.

     Surrounding context such as additional nesting or use of the value
     in a scalar assignment may cause the array to be joined back into
     a single string again.

a
     Sort in array index order; when combined with `O' sort in reverse
     array index order.  Note that `a' is therefore equivalent to the
     default but `Oa' is useful for obtaining an array's elements in
     reverse order.

b
     Quote with backslashes only characters that are special to pattern
     matching. This is useful when the contents of the variable are to
     be tested using GLOB_SUBST, including the ${~...} switch.

     Quoting using one of the q family of flags does not work for this
     purpose since quotes are not stripped from non-pattern characters
     by GLOB_SUBST.  In other words,


          pattern=${(q)str}
          [[ $str = ${~pattern} ]]

     works if $str is `a*b' but not if it is `a b', whereas


          pattern=${(b)str}
          [[ $str = ${~pattern} ]]

     is always true for any possible value of $str.

c
     With ${#NAME}, count the total number of characters in an array,
     as if the elements were concatenated with spaces between them.
     This is not a true join of the array, so other expressions used
     with this flag may have an effect on the elements of the array
     before it is counted.

C
     Capitalize the resulting words.  `Words' in this case refers to
     sequences of alphanumeric characters separated by
     non-alphanumerics, _not_ to words that result from field splitting.

D
     Assume the string or array elements contain directories and attempt
     to substitute the leading part of these by names.  The remainder of
     the path (the whole of it if the leading part was not substituted)
     is then quoted so that the whole string can be used as a shell
     argument.  This is the reverse of `~' substitution:  see *Note
     Filename Expansion::.

e
     Perform single word shell expansions, namely _parameter expansion_,
     _command substitution_ and _arithmetic expansion_, on the result.
     Such expansions can be nested but too deep recursion may have
     unpredictable effects.

f
     Split the result of the expansion at newlines. This is a shorthand
     for `ps:\n:'.

F
     Join the words of arrays together using newline as a separator.
     This is a shorthand for `pj:\n:'.

g:OPTS:
     Process escape sequences like the echo builtin when no options are
     given (g::).  With the o option, octal escapes don't take a leading
     zero.  With the c option, sequences like `^X' are also processed.
     With the e option, processes `\M-t' and similar sequences like the
     print builtin.  With both of the o and e options, behaves like the
     print builtin except that in none of these modes is `\c'
     interpreted.

i
     Sort case-insensitively.  May be combined with `n' or `O'.

k
     If NAME refers to an associative array, substitute the _keys_
     (element names) rather than the values of the elements.  Used with
     subscripts (including ordinary arrays), force indices or keys to be
     substituted even if the subscript form refers to values.  However,
     this flag may not be combined with subscript ranges.  With the
     KSH_ARRAYS option a subscript `[*]' or `[@]' is needed to operate
     on the whole array, as usual.

L
     Convert all letters in the result to lower case.

n
     Sort decimal integers numerically; if the first differing
     characters of two test strings are not digits, sorting is lexical.
     `+' and `-' are not treated specially; they are treated as any
     other non-digit.  Integers with more initial zeroes are sorted
     before those with fewer or none.  Hence the array `foo+24 foo1
     foo02 foo2 foo3 foo20 foo23' is sorted into the order shown.  May
     be combined with `i' or `O'.

-
     As n, but a leading minus sign indicates a negative decimal
     integer.  A leading minus sign not followed by an integer does not
     trigger numeric sorting.  Note that `+' signs are not handled
     specially (this may change in the future).

o
     Sort the resulting words in ascending order; if this appears on its
     own the sorting is lexical and case-sensitive (unless the locale
     renders it case-insensitive).  Sorting in ascending order is the
     default for other forms of sorting, so this is ignored if combined
     with `a', `i', `n' or `-'.

O
     Sort the resulting words in descending order; `O' without `a',
     `i', `n' or `-' sorts in reverse lexical order.  May be combined
     with `a', `i', `n' or `-' to reverse the order of sorting.

P
     This forces the value of the parameter NAME to be interpreted as a
     further parameter name, whose value will be used where appropriate.
     Note that flags set with one of the typeset family of commands (in
     particular case transformations) are not applied to the value of
     NAME used in this fashion.

     If used with a nested parameter or command substitution, the
     result of that will be taken as a parameter name in the same way.
     For example, if you have `foo=bar' and `bar=baz', the strings
     ${(P)foo}, ${(P)${foo}}, and ${(P)$(echo bar)} will be expanded to
     `baz'.

     Likewise, if the reference is itself nested, the expression with
     the flag is treated as if it were directly replaced by the
     parameter name.  It is an error if this nested substitution
     produces an array with more than one word.  For example, if
     `name=assoc' where the parameter assoc is an associative array,
     then `${${(P)name}[elt]}' refers to the element of the associative
     subscripted `elt'.

q
     Quote characters that are special to the shell in the resulting
     words with backslashes; unprintable or invalid characters are
     quoted using the $'\NNN' form, with separate quotes for each octet.

     If this flag is given twice, the resulting words are quoted in
     single quotes and if it is given three times, the words are quoted
     in double quotes; in these forms no special handling of
     unprintable or invalid characters is attempted.  If the flag is
     given four times, the words are quoted in single quotes preceded
     by a $.  Note that in all three of these forms quoting is done
     unconditionally, even if this does not change the way the
     resulting string would be interpreted by the shell.

     If a q- is given (only a single q may appear), a minimal form of
     single quoting is used that only quotes the string if needed to
     protect special characters.  Typically this form gives the most
     readable output.

     If a q+ is given, an extended form of minimal quoting is used that
     causes unprintable characters to be rendered using $'...'.  This
     quoting is similar to that used by the output of values by the
     typeset family of commands.

Q
     Remove one level of quotes from the resulting words.

t
     Use a string describing the type of the parameter where the value
     of the parameter would usually appear. This string consists of
     keywords separated by hyphens (`-'). The first keyword in the
     string describes the main type, it can be one of `scalar',
     `array', `integer', `float' or `association'. The other keywords
     describe the type in more detail:


    local
          for local parameters

    left
          for left justified parameters

    right_blanks
          for right justified parameters with leading blanks

    right_zeros
          for right justified parameters with leading zeros

    lower
          for parameters whose value is converted to all lower case
          when it is expanded

    upper
          for parameters whose value is converted to all upper case
          when it is expanded

    readonly
          for readonly parameters

    tag
          for tagged parameters

    tied
          for parameters tied to another parameter in the manner of PATH
          (colon-separated list) and path (array), whether these are
          special parameters or user-defined with `typeset -T'

    export
          for exported parameters

    unique
          for arrays which keep only the first occurrence of duplicated
          values

    hide
          for parameters with the `hide' flag

    hideval
          for parameters with the `hideval' flag

    special
          for special parameters defined by the shell


u
     Expand only the first occurrence of each unique word.

U
     Convert all letters in the result to upper case.

v
     Used with k, substitute (as two consecutive words) both the key
     and the value of each associative array element.  Used with
     subscripts, force values to be substituted even if the subscript
     form refers to indices or keys.

V
     Make any special characters in the resulting words visible.

w
     With ${#NAME}, count words in arrays or strings; the s flag may be
     used to set a word delimiter.

W
     Similar to w with the difference that empty words between repeated
     delimiters are also counted.

X
     With this flag, parsing errors occurring with the Q, e and # flags
     or the pattern matching forms such as `${NAME#PATTERN}' are
     reported.  Without the flag, errors are silently ignored.

z
     Split the result of the expansion into words using shell parsing to
     find the words, i.e. taking into account any quoting in the value.
     Comments are not treated specially but as ordinary strings, similar
     to interactive shells with the INTERACTIVE_COMMENTS option unset
     (however, see the Z flag below for related options)

     Note that this is done very late, even later than the `(s)' flag.
     So to access single words in the result use nested expansions as
     in `${${(z)foo}[2]}'. Likewise, to remove the quotes in the
     resulting words use `${(Q)${(z)foo}}'.

0
     Split the result of the expansion on null bytes.  This is a
     shorthand for `ps:\0:'.


The following flags (except p) are followed by one or more arguments as
shown.  Any character, or the matching pairs `(...)', `{...}', `[...]',
or `<...>', may be used in place of a colon as delimiters, but note
that when a flag takes more than one argument, a matched pair of
delimiters must surround each argument.


p
     Recognize the same escape sequences as the print builtin in string
     arguments to any of the flags described below that follow this
     argument.

     Alternatively, with this option string arguments may be in the form
     $VAR in which case the value of the variable is substituted.  Note
     this form is strict; the string argument does not undergo general
     parameter expansion.

     For example,


          sep=:
          val=a:b:c
          print ${(ps.$sep.)val}

     splits the variable on a :.

~
     Strings inserted into the expansion by any of the flags below are
     to be treated as patterns.  This applies to the string arguments
     of flags that follow ~ within the same set of parentheses.
     Compare with ~ outside parentheses, which forces the entire
     substituted string to be treated as a pattern.  Hence, for example,


          [[ "?" = ${(~j.|.)array} ]]

     treats `|' as a pattern and succeeds if and only if $array
     contains the string `?' as an element.  The ~ may be repeated to
     toggle the behaviour; its effect only lasts to the end of the
     parenthesised group.

j:STRING:
     Join the words of arrays together using STRING as a separator.  Note
     that this occurs before field splitting by the s:STRING: flag or
     the SH_WORD_SPLIT option.

l:EXPR::STRING1::STRING2:
     Pad the resulting words on the left.  Each word will be truncated
     if required and placed in a field EXPR characters wide.

     The arguments :STRING1: and :STRING2: are optional; neither, the
     first, or both may be given.  Note that the same pairs of
     delimiters must be used for each of the three arguments.  The
     space to the left will be filled with STRING1 (concatenated as
     often as needed) or spaces if STRING1 is not given.  If both
     STRING1 and STRING2 are given, STRING2 is inserted once directly
     to the left of each word, truncated if necessary, before STRING1
     is used to produce any remaining padding.

     If either of STRING1 or STRING2 is present but empty, i.e. there
     are two delimiters together at that point, the first character of
     $IFS is used instead.

     If the MULTIBYTE option is in effect, the flag m may also be
     given, in which case widths will be used for the calculation of
     padding; otherwise individual multibyte characters are treated as
     occupying one unit of width.

     If the MULTIBYTE option is not in effect, each byte in the string
     is treated as occupying one unit of width.

     Control characters are always assumed to be one unit wide; this
     allows the mechanism to be used for generating repetitions of
     control characters.

m
     Only useful together with one of the flags l or r or with the #
     length operator when the MULTIBYTE option is in effect.  Use the
     character width reported by the system in calculating how much of
     the string it occupies or the overall length of the string.  Most
     printable characters have a width of one unit, however certain
     Asian character sets and certain special effects use wider
     characters; combining characters have zero width.  Non-printable
     characters are arbitrarily counted as zero width; how they would
     actually be displayed will vary.

     If the m is repeated, the character either counts zero (if it has
     zero width), else one.  For printable character strings this has
     the effect of counting the number of glyphs (visibly separate
     characters), except for the case where combining characters
     themselves have non-zero width (true in certain alphabets).

r:EXPR::STRING1::STRING2:
     As l, but pad the words on the right and insert STRING2
     immediately to the right of the string to be padded.

     Left and right padding may be used together.  In this case the
     strategy is to apply left padding to the first half width of each
     of the resulting words, and right padding to the second half.  If
     the string to be padded has odd width the extra padding is applied
     on the left.

s:STRING:
     Force field splitting at the separator STRING.  Note that a STRING
     of two or more characters means that all of them must match in
     sequence; this differs from the treatment of two or more
     characters in the IFS parameter.  See also the = flag and the
     SH_WORD_SPLIT option.  An empty string may also be given in which
     case every character will be a separate element.

     For historical reasons, the usual behaviour that empty array
     elements are retained inside double quotes is disabled for arrays
     generated by splitting; hence the following:


          line="one::three"
          print -l "${(s.:.)line}"

     produces two lines of output for one and three and elides the
     empty field.  To override this behaviour, supply the `(@)' flag as
     well, i.e.  "${(@s.:.)line}".

Z:OPTS:
     As z but takes a combination of option letters between a following
     pair of delimiter characters.  With no options the effect is
     identical to z.  The following options are available:


    (Z+c+)
          causes comments to be parsed as a string and retained; any
          field in the resulting array beginning with an unquoted
          comment character is a comment.

    (Z+C+)
          causes comments to be parsed and removed.  The rule for
          comments is standard: anything between a word starting with
          the third character of $HISTCHARS, default #, up to the next
          newline is a comment.

    (Z+n+)
          causes unquoted newlines to be treated as ordinary
          whitespace, else they are treated as if they are shell code
          delimiters and converted to semicolons.


     Options are combined within the same set of delimiters, e.g.
     (Z+Cn+).

_:FLAGS:
     The underscore (_) flag is reserved for future use.  As of this
     revision of zsh, there are no valid FLAGS; anything following an
     underscore, other than an empty pair of delimiters, is treated as
     an error, and the flag itself has no effect.


The following flags are meaningful with the ${...#...} or ${...%...}
forms.  The S, I, and * flags may also be used with the ${.../...}
forms.


S
     With # or ##, search for the match that starts closest to the
     start of the string (a `substring match'). Of all matches at a
     particular position, # selects the shortest and ## the longest:


          % str="aXbXc"
          % echo ${(S)str#X*}
          abXc
          % echo ${(S)str##X*}
          a
          %

     With % or %%, search for the match that starts closest to the end
     of the string:


          % str="aXbXc"
          % echo ${(S)str%X*}
          aXbc
          % echo ${(S)str%%X*}
          aXb
          %

     (Note that % and %% don't search for the match that ends closest
     to the end of the string, as one might expect.)

     With substitution via ${.../...} or ${...//...}, specifies
     non-greedy matching, i.e. that the shortest instead of the longest
     match should be replaced:


          % str="abab"
          % echo ${str/*b/_}
          _
          % echo ${(S)str/*b/_}
          _ab
          %

I:EXPR:
     Search the EXPRth match (where EXPR evaluates to a number).  This
     only applies when searching for substrings, either with the S
     flag, or with ${.../...} (only the EXPRth match is substituted) or
     ${...//...} (all matches from the EXPRth on are substituted).  The
     default is to take the first match.

     The EXPRth match is counted such that there is either one or zero
     matches from each starting position in the string, although for
     global substitution matches overlapping previous replacements are
     ignored.  With the ${...%...} and ${...%%...} forms, the starting
     position for the match moves backwards from the end as the index
     increases, while with the other forms it moves forward from the
     start.

     Hence with the string
          which switch is the right switch for Ipswich?
     substitutions of the form ${(SI:N:)string#w*ch} as N increases
     from 1 will match and remove `which', `witch', `witch' and `wich';
     the form using `##' will match and remove `which switch is the
     right switch for Ipswich', `witch is the right switch for
     Ipswich', `witch for Ipswich' and `wich'. The form using `%' will
     remove the same matches as for `#', but in reverse order, and the
     form using `%%' will remove the same matches as for `##' in reverse
     order.

*
     Enable EXTENDED_GLOB for substitution via ${.../...} or
     ${...//...}.  Note that `**' does not disable extendedglob.

B
     Include the index of the beginning of the match in the result.

E
     Include the index one character past the end of the match in the
     result (note this is inconsistent with other uses of parameter
     index).

M
     Include the matched portion in the result.

N
     Include the length of the match in the result.

R
     Include the unmatched portion in the result (the _R_est).



14.3.2 Rules
------------

Here is a summary of the rules for substitution; this assumes that
braces are present around the substitution, i.e. ${...}.  Some
particular examples are given below.  Note that the Zsh Development
Group accepts _no responsibility_ for any brain damage which may occur
during the reading of the following rules.


1. _Nested substitution_
     If multiple nested ${...} forms are present, substitution is
     performed from the inside outwards.  At each level, the
     substitution takes account of whether the current value is a
     scalar or an array, whether the whole substitution is in double
     quotes, and what flags are supplied to the current level of
     substitution, just as if the nested substitution were the
     outermost.  The flags are not propagated up to enclosing
     substitutions; the nested substitution will return either a scalar
     or an array as determined by the flags, possibly adjusted for
     quoting.  All the following steps take place where applicable at
     all levels of substitution.

     Note that, unless the `(P)' flag is present, the flags and any
     subscripts apply directly to the value of the nested substitution;
     for example, the expansion ${${foo}} behaves exactly the same as
     ${foo}.  When the `(P)' flag is present in a nested substitution,
     the other substitution rules are applied to the value _before_ it
     is interpreted as a name, so ${${(P)foo}} may differ from
     ${(P)foo}.

     At each nested level of substitution, the substituted words
     undergo all forms of single-word substitution (i.e. not filename
     generation), including command substitution, arithmetic expansion
     and filename expansion (i.e. leading ~ and =).  Thus, for example,
     ${${:-=cat}:h} expands to the directory where the cat program
     resides.  (Explanation: the internal substitution has no parameter
     but a default value =cat, which is expanded by filename expansion
     to a full path; the outer substitution then applies the modifier
     :h and takes the directory part of the path.)

2. _Internal parameter flags_
     Any parameter flags set by one of the typeset family of commands,
     in particular the -L, -R, -Z, -u and -l options for padding and
     capitalization, are applied directly to the parameter value.  Note
     these flags are options to the command, e.g. `typeset -Z'; they
     are not the same as the flags used within parameter substitutions.

     At the outermost level of substitution, the `(P)' flag (rule 4.)
     ignores these transformations and uses the unmodified value of the
     parameter as the name to be replaced.  This is usually the desired
     behavior because padding may make the value syntactically illegal
     as a parameter name, but if capitalization changes are desired,
     use the ${${(P)foo}} form (rule 25.).

3. _Parameter subscripting_
     If the value is a raw parameter reference with a subscript, such as
     ${VAR[3]}, the effect of subscripting is applied directly to the
     parameter.  Subscripts are evaluated left to right; subsequent
     subscripts apply to the scalar or array value yielded by the
     previous subscript.  Thus if var is an array, ${var[1][2]} is the
     second character of the first word, but ${var[2,4][2]} is the
     entire third word (the second word of the range of words two
     through four of the original array).  Any number of subscripts may
     appear.  Flags such as `(k)' and `(v)' which alter the result of
     subscripting are applied.

4. _Parameter name replacement_
     At the outermost level of nesting only, the `(P)' flag is applied.
     This treats the value so far as a parameter name (which may
     include a subscript expression) and replaces that with the
     corresponding value.  This replacement occurs later if the `(P)'
     flag appears in a nested substitution.

     If the value so far names a parameter that has internal flags
     (rule 2.), those internal flags are applied to the new value after
     replacement.

5. _Double-quoted joining_
     If the value after this process is an array, and the substitution
     appears in double quotes, and neither an `(@)' flag nor a `#'
     length operator is present at the current level, then words of the
     value are joined with the first character of the parameter $IFS,
     by default a space, between each word (single word arrays are not
     modified).  If the `(j)' flag is present, that is used for joining
     instead of $IFS.

6. _Nested subscripting_
     Any remaining subscripts (i.e. of a nested substitution) are
     evaluated at this point, based on whether the value is an array or
     a scalar.  As with 3., multiple subscripts can appear.  Note that
     ${foo[2,4][2]} is thus equivalent to ${${foo[2,4]}[2]} and also to
     "${${(@)foo[2,4]}[2]}" (the nested substitution returns an array in
     both cases), but not to "${${foo[2,4]}[2]}" (the nested
     substitution returns a scalar because of the quotes).

7. _Modifiers_
     Any modifiers, as specified by a trailing `#', `%', `/' (possibly
     doubled) or by a set of modifiers of the form `:...' (see *Note
     Modifiers:: in *Note History Expansion::), are applied to the words
     of the value at this level.

8. _Character evaluation_
     Any `(#)' flag is applied, evaluating the result so far numerically
     as a character.

9. _Length_
     Any initial `#' modifier, i.e. in the form ${#VAR}, is used to
     evaluate the length of the expression so far.

10. _Forced joining_
     If the `(j)' flag is present, or no `(j)' flag is present but the
     string is to be split as given by rule 11., and joining did not
     take place at rule 5., any words in the value are joined together
     using the given string or the first character of $IFS if none.
     Note that the `(F)' flag implicitly supplies a string for joining
     in this manner.

11. _Simple word splitting_
     If one of the `(s)' or `(f)' flags are present, or the `='
     specifier was present (e.g. ${=VAR}), the word is split on
     occurrences of the specified string, or (for = with neither of the
     two flags present) any of the characters in $IFS.

     If no `(s)', `(f)' or `=' was given, but the word is not quoted
     and the option SH_WORD_SPLIT is set, the word is split on
     occurrences of any of the characters in $IFS.  Note this step, too,
     takes place at all levels of a nested substitution.

12. _Case modification_
     Any case modification from one of the flags `(L)', `(U)' or `(C)'
     is applied.

13. _Escape sequence replacement_
     First any replacements from the `(g)' flag are performed, then any
     prompt-style formatting from the `(%)' family of flags is applied.

14. _Quote application_
     Any quoting or unquoting using `(q)' and `(Q)' and related flags
     is applied.

15. _Directory naming_
     Any directory name substitution using `(D)' flag is applied.

16. _Visibility enhancement_
     Any modifications to make characters visible using the `(V)' flag
     are applied.

17. _Lexical word splitting_
     If the '(z)' flag or one of the forms of the '(Z)' flag is
     present, the word is split as if it were a shell command line, so
     that quotation marks and other metacharacters are used to decide
     what constitutes a word.  Note this form of splitting is entirely
     distinct from that described by rule 11.: it does not use $IFS, and
     does not cause forced joining.

18. _Uniqueness_
     If the result is an array and the `(u)' flag was present, duplicate
     elements are removed from the array.

19. _Ordering_
     If the result is still an array and one of the `(o)' or `(O)' flags
     was present, the array is reordered.

20. RC_EXPAND_PARAM
     At this point the decision is made whether any resulting array
     elements are to be combined element by element with surrounding
     text, as given by either the RC_EXPAND_PARAM option or the `^'
     flag.

21. _Re-evaluation_
     Any `(e)' flag is applied to the value, forcing it to be
     re-examined for new parameter substitutions, but also for command
     and arithmetic substitutions.

22. _Padding_
     Any padding of the value by the `(l.FILL.)' or `(r.FILL.)' flags
     is applied.

23. _Semantic joining_
     In contexts where expansion semantics requires a single word to
     result, all words are rejoined with the first character of IFS
     between.  So in `${(P)${(f)lines}}' the value of ${lines} is split
     at newlines, but then must be joined again before the `(P)' flag
     can be applied.

     If a single word is not required, this rule is skipped.

24. _Empty argument removal_
     If the substitution does not appear in double quotes, any resulting
     zero-length argument, whether from a scalar or an element of an
     array, is elided from the list of arguments inserted into the
     command line.

     Strictly speaking, the removal happens later as the same happens
     with other forms of substitution; the point to note here is simply
     that it occurs after any of the above parameter operations.

25. _Nested parameter name replacement_
     If the `(P)' flag is present and rule 4. has not applied, the
     value so far is treated as a parameter name (which may include a
     subscript expression) and replaced with the corresponding value,
     with internal flags (rule 2.) applied to the new value.



14.3.3 Examples
---------------

The flag f is useful to split a double-quoted substitution line by
line.  For example, ${(f)"$(<FILE)"} substitutes the contents of FILE
divided so that each line is an element of the resulting array.
Compare this with the effect of $(<FILE) alone, which divides the file
up by words, or the same inside double quotes, which makes the entire
content of the file a single string.

The following illustrates the rules for nested parameter expansions.
Suppose that $foo contains the array (bar baz):


"${(@)${foo}[1]}"
     This produces the result b.  First, the inner substitution
     "${foo}", which has no array (@) flag, produces a single word
     result "bar baz".  The outer substitution "${(@)...[1]}" detects
     that this is a scalar, so that (despite the `(@)' flag) the
     subscript picks the first character.

"${${(@)foo}[1]}"
     This produces the result `bar'.  In this case, the inner
     substitution "${(@)foo}" produces the array `(bar baz)'.  The outer
     substitution "${...[1]}" detects that this is an array and picks
     the first word.  This is similar to the simple case "${foo[1]}".


As an example of the rules for word splitting and joining, suppose $foo
contains the array `(ax1 bx1)'.  Then


${(s/x/)foo}
     produces the words `a', `1 b' and `1'.

${(j/x/s/x/)foo}
     produces `a', `1', `b' and `1'.

${(s/x/)foo%%1*}
     produces `a' and ` b' (note the extra space).  As substitution
     occurs before either joining or splitting, the operation  first
     generates the modified array (ax bx), which is joined to give "ax
     bx", and then split to give `a', ` b' and `'.  The final empty
     string will then be elided, as it is not in double quotes.




File: zsh.info,  Node: Command Substitution,  Next: Arithmetic Expansion,  Prev: Parameter Expansion,  Up: Expansion

14.4 Command Substitution
=========================

A command enclosed in parentheses preceded by a dollar sign, like
`$(...)', or quoted with grave accents, like ``...`', is replaced with
its standard output, with any trailing newlines deleted.  If the
substitution is not enclosed in double quotes, the output is broken
into words using the IFS parameter.  

The substitution `$(cat FOO)' may be replaced by the faster `$(<FOO)'.
In this case FOO undergoes single word shell expansions (_parameter
expansion_, _command substitution_ and _arithmetic expansion_), but not
filename generation.

If the option GLOB_SUBST is set, the result of any unquoted command
substitution, including the special form just mentioned, is eligible for
filename generation.




File: zsh.info,  Node: Arithmetic Expansion,  Next: Brace Expansion,  Prev: Command Substitution,  Up: Expansion

14.5 Arithmetic Expansion
=========================

A string of the form `$[EXP]' or `$((EXP))' is substituted with the
value of the arithmetic expression EXP.  EXP is subjected to _parameter
expansion_, _command substitution_ and _arithmetic expansion_ before it
is evaluated.  See *Note Arithmetic Evaluation::.


File: zsh.info,  Node: Brace Expansion,  Next: Filename Expansion,  Prev: Arithmetic Expansion,  Up: Expansion

14.6 Brace Expansion
====================

A string of the form `FOO{XX,YY,ZZ}BAR' is expanded to the individual
words `FOOXXBAR', `FOOYYBAR' and `FOOZZBAR'.  Left-to-right order is
preserved.  This construct may be nested.  Commas may be quoted in
order to include them literally in a word.

An expression of the form `{N1..N2}', where N1 and N2 are integers, is
expanded to every number between N1 and N2 inclusive.  If either number
begins with a zero, all the resulting numbers will be padded with
leading zeroes to that minimum width, but for negative numbers the -
character is also included in the width.  If the numbers are in
decreasing order the resulting sequence will also be in decreasing
order.

An expression of the form `{N1..N2..N3}', where N1, N2, and N3 are
integers, is expanded as above, but only every N3th number starting
from N1 is output.  If N3 is negative the numbers are output in reverse
order, this is slightly different from simply swapping N1 and N2 in the
case that the step N3 doesn't evenly divide the range.  Zero padding
can be specified in any of the three numbers, specifying it in the
third can be useful to pad for example `{-99..100..01}' which is not
possible to specify by putting a 0 on either of the first two numbers
(i.e. pad to two characters).

An expression of the form `{C1..C2}', where C1 and C2 are single
characters (which may be multibyte characters), is expanded to every
character in the range from C1 to C2 in whatever character sequence is
used internally.  For characters with code points below 128 this is US
ASCII (this is the only case most users will need).  If any intervening
character is not printable, appropriate quotation is used to render it
printable.  If the character sequence is reversed, the output is in
reverse order, e.g. `{d..a}' is substituted as `d c b a'.

If a brace expression matches none of the above forms, it is left
unchanged, unless the option BRACE_CCL (an abbreviation for `brace
character class') is set.  In that case, it is expanded to a list of
the individual characters between the braces sorted into the order of
the characters in the ASCII character set (multibyte characters are not
currently handled).  The syntax is similar to a [...] expression in
filename generation: `-' is treated specially to denote a range of
characters, but `^' or `!' as the first character is treated normally.
For example, `{abcdef0-9}' expands to 16 words 0 1 2 3 4 5 6 7 8 9 a b
c d e f.

Note that brace expansion is not part of filename generation
(globbing); an expression such as */{foo,bar} is split into two
separate words */foo and */bar before filename generation takes place.
In particular, note that this is liable to produce a `no match' error if
_either_ of the two expressions does not match; this is to be contrasted
with */(foo|bar), which is treated as a single pattern but otherwise
has similar effects.

To combine brace expansion with array expansion, see the ${^SPEC} form
described in *Note Parameter Expansion:: above.




File: zsh.info,  Node: Filename Expansion,  Next: Filename Generation,  Prev: Brace Expansion,  Up: Expansion

14.7 Filename Expansion
=======================

Each word is checked to see if it begins with an unquoted `~'.  If it
does, then the word up to a `/', or the end of the word if there is no
`/', is checked to see if it can be substituted in one of the ways
described here.  If so, then the `~' and the checked portion are
replaced with the appropriate substitute value.

A `~' by itself is replaced by the value of $HOME.  A `~' followed by a
`+' or a `-' is replaced by current or previous working directory,
respectively.

A `~' followed by a number is replaced by the directory at that
position in the directory stack.  `~0' is equivalent to `~+', and `~1'
is the top of the stack.  `~+' followed by a number is replaced by the
directory at that position in the directory stack.  `~+0' is equivalent
to `~+', and `~+1' is the top of the stack.  `~-' followed by a number
is replaced by the directory that many positions from the bottom of the
stack.  `~-0' is the bottom of the stack.  The PUSHD_MINUS option
exchanges the effects of `~+' and `~-' where they are followed by a
number.



* Menu:

* Dynamic named directories::
* Static named directories::
* `=' expansion::
* Notes::



File: zsh.info,  Node: Dynamic named directories,  Next: Static named directories,  Up: Filename Expansion

14.7.1 Dynamic named directories
--------------------------------

If the function zsh_directory_name exists, or the shell variable
zsh_directory_name_functions exists and contains an array of function
names, then the functions are used to implement dynamic directory
naming.  The functions are tried in order until one returns status
zero, so it is important that functions test whether they can handle
the case in question and return an appropriate status.

A `~' followed by a string NAMSTR in unquoted square brackets is
treated specially as a dynamic directory name.  Note that the first
unquoted closing square bracket always terminates NAMSTR.  The shell
function is passed two arguments: the string n (for name) and NAMSTR.
It should either set the array reply to a single element which is the
directory corresponding to the name and return status zero (executing
an assignment as the last statement is usually sufficient), or it
should return status non-zero.  In the former case the element of reply
is used as the directory; in the latter case the substitution is deemed
to have failed.  If all functions fail and the option NOMATCH is set,
an error results.

The functions defined as above are also used to see if a directory can
be turned into a name, for example when printing the directory stack or
when expanding %~ in prompts.  In this case each function is passed two
arguments: the string d (for directory) and the candidate for dynamic
naming.  The function should either return non-zero status, if the
directory cannot be named by the function, or it should set the array
reply to consist of two elements: the first is the dynamic name for the
directory (as would appear within `~[...]'), and the second is the
prefix length of the directory to be replaced.  For example, if the
trial directory is /home/myname/src/zsh and the dynamic name for
/home/myname/src (which has 16 characters) is s, then the function sets


     reply=(s 16)

The directory name so returned is compared with possible static names
for parts of the directory path, as described below; it is used if the
prefix length matched (16 in the example) is longer than that matched
by any static name.

It is not a requirement that a function implements both n and d calls;
for example, it might be appropriate for certain dynamic forms of
expansion not to be contracted to names.  In that case any call with
the first argument d should cause a non-zero status to be returned.

The completion system calls `zsh_directory_name c' followed by
equivalent calls to elements of the array zsh_directory_name_functions,
if it exists, in order to complete dynamic names for directories.  The
code for this should be as for any other completion function as
described in *Note Completion System::.

As a working example, here is a function that expands any dynamic names
beginning with the string p: to directories below /home/pws/perforce.
In this simple case a static name for the directory would be just as
effective.


     zsh_directory_name() {
       emulate -L zsh
       setopt extendedglob
       local -a match mbegin mend
       if [[ $1 = d ]]; then
         # turn the directory into a name
         if [[ $2 = (#b)(/home/pws/perforce/)([^/]##)* ]]; then
           typeset -ga reply
           reply=(p:$match[2] $(( ${#match[1]} + ${#match[2]} )) )
         else
           return 1
         fi
       elif [[ $1 = n ]]; then
         # turn the name into a directory
         [[ $2 != (#b)p:(?*) ]] && return 1
         typeset -ga reply
         reply=(/home/pws/perforce/$match[1])
       elif [[ $1 = c ]]; then
         # complete names
         local expl
         local -a dirs
         dirs=(/home/pws/perforce/*(/:t))
         dirs=(p:${^dirs})
         _wanted dynamic-dirs expl 'dynamic directory' compadd -S\] -a dirs
         return
       else
         return 1
       fi
       return 0
     }



File: zsh.info,  Node: Static named directories,  Next: `=' expansion,  Prev: Dynamic named directories,  Up: Filename Expansion

14.7.2 Static named directories
-------------------------------

A `~' followed by anything not already covered consisting of any number
of alphanumeric characters or underscore (`_'), hyphen (`-'), or dot
(`.') is looked up as a named directory, and replaced by the value of
that named directory if found.  Named directories are typically home
directories for users on the system.  They may also be defined if the
text after the `~' is the name of a string shell parameter whose value
begins with a `/'.  Note that trailing slashes will be removed from the
path to the directory (though the original parameter is not modified).

It is also possible to define directory names using the -d option to the
hash builtin.

When the shell prints a path (e.g. when expanding %~ in prompts or when
printing the directory stack), the path is checked to see if it has a
named directory as its prefix.  If so, then the prefix portion is
replaced with a `~' followed by the name of the directory.  The shorter
of the two ways of referring to the directory is used, i.e. either the
directory name or the full path; the name is used if they are the same
length.  The parameters $PWD and $OLDPWD are never abbreviated in this
fashion.




File: zsh.info,  Node: `=' expansion,  Next: Notes,  Prev: Static named directories,  Up: Filename Expansion

14.7.3 `=' expansion
--------------------

If a word begins with an unquoted `=' and the EQUALS option is set, the
remainder of the word is taken as the name of a command.  If a command
exists by that name, the word is replaced by the full pathname of the
command.




File: zsh.info,  Node: Notes,  Prev: `=' expansion,  Up: Filename Expansion

14.7.4 Notes
------------

Filename expansion is performed on the right hand side of a parameter
assignment, including those appearing after commands of the typeset
family.  In this case, the right hand side will be treated as a
colon-separated list in the manner of the PATH parameter, so that a `~'
or an `=' following a `:' is eligible for expansion.  All such
behaviour can be disabled by quoting the `~', the `=', or the whole
expression (but not simply the colon); the EQUALS option is also
respected.

If the option MAGIC_EQUAL_SUBST is set, any unquoted shell argument in
the form `IDENTIFIER=EXPRESSION' becomes eligible for file expansion as
described in the previous paragraph.  Quoting the first `=' also
inhibits this.




File: zsh.info,  Node: Filename Generation,  Prev: Filename Expansion,  Up: Expansion

14.8 Filename Generation
========================

If a word contains an unquoted instance of one of the characters `*',
`(', `|', `<', `[', or `?', it is regarded as a pattern for filename
generation, unless the GLOB option is unset.  If the EXTENDED_GLOB
option is set, the `^' and `#' characters also denote a pattern;
otherwise they are not treated specially by the shell.

The word is replaced with a list of sorted filenames that match the
pattern.  If no matching pattern is found, the shell gives an error
message, unless the NULL_GLOB option is set, in which case the word is
deleted; or unless the NOMATCH option is unset, in which case the word
is left unchanged.  

In filename generation, the character `/' must be matched explicitly;
also, a `.' must be matched explicitly at the beginning of a pattern or
after a `/', unless the GLOB_DOTS option is set.  No filename
generation pattern matches the files `.' or `..'.  In other instances
of pattern matching, the `/' and `.' are not treated specially.

14.8.1 Glob Operators
---------------------


*
     Matches any string, including the null string.

?
     Matches any character.

[...]
     Matches any of the enclosed characters.  Ranges of characters can
     be specified by separating two characters by a `-'.  A `-' or `]'
     may be matched by including it as the first character in the list.  There
     are also several named classes of characters, in the form
     `[:NAME:]' with the following meanings.  The first set use the
     macros provided by the operating system to test for the given
     character combinations, including any modifications due to local
     language settings, see ctype(3):


    [:alnum:]
          The character is alphanumeric

    [:alpha:]
          The character is alphabetic

    [:ascii:]
          The character is 7-bit, i.e. is a single-byte character
          without the top bit set.

    [:blank:]
          The character is a blank character

    [:cntrl:]
          The character is a control character

    [:digit:]
          The character is a decimal digit

    [:graph:]
          The character is a printable character other than whitespace

    [:lower:]
          The character is a lowercase letter

    [:print:]
          The character is printable

    [:punct:]
          The character is printable but neither alphanumeric nor
          whitespace

    [:space:]
          The character is whitespace

    [:upper:]
          The character is an uppercase letter

    [:xdigit:]
          The character is a hexadecimal digit


     Another set of named classes is handled internally by the shell and
     is not sensitive to the locale:


    [:IDENT:]
          The character is allowed to form part of a shell identifier,
          such as a parameter name; this test respects the
          POSIX_IDENTIFIERS option

    [:IFS:]
          The character is used as an input field separator, i.e. is
          contained in the IFS parameter

    [:IFSSPACE:]
          The character is an IFS white space character; see the
          documentation for IFS in *Note Parameters Used By The Shell::.

    [:INCOMPLETE:]
          Matches a byte that starts an incomplete multibyte character.
          Note that there may be a sequence of more than one bytes that
          taken together form the prefix of a multibyte character.  To
          test for a potentially incomplete byte sequence, use the
          pattern `[[:INCOMPLETE:]]*'.  This will never match a
          sequence starting with a valid multibyte character.

    [:INVALID:]
          Matches a byte that does not start a valid multibyte
          character.  Note this may be a continuation byte of an
          incomplete multibyte character as any part of a multibyte
          string consisting of invalid and incomplete multibyte
          characters is treated as single bytes.

    [:WORD:]
          The character is treated as part of a word; this test is
          sensitive to the value of the WORDCHARS parameter


     Note that the square brackets are additional to those enclosing
     the whole set of characters, so to test for a single alphanumeric
     character you need `[[:alnum:]]'.  Named character sets can be
     used alongside other types, e.g. `[[:alpha:]0-9]'.

[^...]
[!...]
     Like [...], except that it matches any character which is not in
     the given set.

<[X]-[Y]>
     Matches any number in the range X to Y, inclusive.  Either of the
     numbers may be omitted to make the range open-ended; hence `<->'
     matches any number.  To match individual digits, the [...] form is
     more efficient.

     Be careful when using other wildcards adjacent to patterns of this
     form; for example, <0-9>* will actually match any number
     whatsoever at the start of the string, since the `<0-9>' will
     match the first digit, and the `*' will match any others.  This is
     a trap for the unwary, but is in fact an inevitable consequence of
     the rule that the longest possible match always succeeds.
     Expressions such as `<0-9>[^[:digit:]]*' can be used instead.

(...)
     Matches the enclosed pattern.  This is used for grouping.  If the
     KSH_GLOB option is set, then a `@', `*', `+', `?' or `!'
     immediately preceding the `(' is treated specially, as detailed
     below. The option SH_GLOB prevents bare parentheses from being
     used in this way, though the KSH_GLOB option is still available.

     Note that grouping cannot extend over multiple directories: it is
     an error to have a `/' within a group (this only applies for
     patterns used in filename generation).  There is one exception:  a
     group of the form (PAT/)# appearing as a complete path segment can
     match a sequence of directories.  For example, foo/(a*/)#bar
     matches foo/bar, foo/any/bar, foo/any/anyother/bar, and so on.

X|Y
     Matches either X or Y.  This operator has lower precedence than
     any other.  The `|' character must be within parentheses, to avoid
     interpretation as a pipeline.  The alternatives are tried in order
     from left to right.

^X
     (Requires EXTENDED_GLOB to be set.)  Matches anything except the
     pattern X.  This has a higher precedence than `/', so `^foo/bar'
     will search directories in `.' except `./foo' for a file named
     `bar'.

X~Y
     (Requires EXTENDED_GLOB to be set.)  Match anything that matches
     the pattern X but does not match Y.  This has lower precedence
     than any operator except `|', so `*/*~foo/bar' will search for all
     files in all directories in `.'  and then exclude `foo/bar' if
     there was such a match.  Multiple patterns can be excluded by
     `FOO~BAR~BAZ'.  In the exclusion pattern (Y), `/' and `.' are not
     treated specially the way they usually are in globbing.

X#
     (Requires EXTENDED_GLOB to be set.)  Matches zero or more
     occurrences of the pattern X.  This operator has high precedence;
     `12#' is equivalent to `1(2#)', rather than `(12)#'.  It is an
     error for an unquoted `#' to follow something which cannot be
     repeated; this includes an empty string, a pattern already
     followed by `##', or parentheses when part of a KSH_GLOB pattern
     (for example, `!(FOO)#' is invalid and must be replaced by
     `*(!(FOO))').

X##
     (Requires EXTENDED_GLOB to be set.)  Matches one or more
     occurrences of the pattern X.  This operator has high precedence;
     `12##' is equivalent to `1(2##)', rather than `(12)##'.  No more
     than two active `#' characters may appear together.  (Note the
     potential clash with glob qualifiers in the form `1(2##)' which
     should therefore be avoided.)


14.8.2 ksh-like Glob Operators
------------------------------

If the KSH_GLOB option is set, the effects of parentheses can be
modified by a preceding `@', `*', `+', `?' or `!'.  This character need
not be unquoted to have special effects, but the `(' must be.


@(...)
     Match the pattern in the parentheses.  (Like `(...)'.)

*(...)
     Match any number of occurrences.  (Like `(...)#', except that
     recursive directory searching is not supported.)

+(...)
     Match at least one occurrence.  (Like `(...)##', except that
     recursive directory searching is not supported.)

?(...)
     Match zero or one occurrence.  (Like `(|...)'.)

!(...)
     Match anything but the expression in parentheses.  (Like
     `(^(...))'.)


14.8.3 Precedence
-----------------

The precedence of the operators given above is (highest) `^', `/', `~',
`|' (lowest); the remaining operators are simply treated from left to
right as part of a string, with `#' and `##' applying to the shortest
possible preceding unit (i.e. a character, `?', `[...]', `<...>', or a
parenthesised expression).  As mentioned above, a `/' used as a
directory separator may not appear inside parentheses, while a `|' must
do so; in patterns used in other contexts than filename generation (for
example, in case statements and tests within `[[...]]'), a `/' is not
special; and `/' is also not special after a `~' appearing outside
parentheses in a filename pattern.

14.8.4 Globbing Flags
---------------------

There are various flags which affect any text to their right up to the
end of the enclosing group or to the end of the pattern; they require
the EXTENDED_GLOB option. All take the form (#X) where X may have one
of the following forms:


i
     Case insensitive:  upper or lower case characters in the pattern
     match upper or lower case characters.

l
     Lower case characters in the pattern match upper or lower case
     characters; upper case characters in the pattern still only match
     upper case characters.

I
     Case sensitive:  locally negates the effect of i or l from that
     point on.

b
     Activate backreferences for parenthesised groups in the pattern;
     this does not work in filename generation.  When a pattern with a
     set of active parentheses is matched, the strings matched by the
     groups are stored in the array $match, the indices of the
     beginning of the matched parentheses in the array $mbegin, and the
     indices of the end in the array $mend, with the first element of
     each array corresponding to the first parenthesised group, and so
     on.  These arrays are not otherwise special to the shell.  The
     indices use the same convention as does parameter substitution, so
     that elements of $mend and $mbegin may be used in subscripts; the
     KSH_ARRAYS option is respected.  Sets of globbing flags are not
     considered parenthesised groups; only the first nine active
     parentheses can be referenced.

     For example,


          foo="a_string_with_a_message"
          if [[ $foo = (a|an)_(#b)(*) ]]; then
            print ${foo[$mbegin[1],$mend[1]]}
          fi

     prints `string_with_a_message'.  Note that the first set of
     parentheses is before the (#b) and does not create a backreference.

     Backreferences work with all forms of pattern matching other than
     filename generation, but note that when performing matches on an
     entire array, such as ${ARRAY#PATTERN}, or a global substitution,
     such as ${PARAM//PAT/REPL}, only the data for the last match
     remains available.  In the case of global replacements this may
     still be useful.  See the example for the m flag below.

     The numbering of backreferences strictly follows the order of the
     opening parentheses from left to right in the pattern string,
     although sets of parentheses may be nested.  There are special
     rules for parentheses followed by `#' or `##'.  Only the last
     match of the parenthesis is remembered: for example, in `[[ abab =
     (#b)([ab])# ]]', only the final `b' is stored in match[1].  Thus
     extra parentheses may be necessary to match the complete segment:
     for example, use `X((ab|cd)#)Y' to match a whole string of either
     `ab' or `cd' between `X' and `Y', using the value of $match[1]
     rather than $match[2].

     If the match fails none of the parameters is altered, so in some
     cases it may be necessary to initialise them beforehand.  If some
     of the backreferences fail to match -- which happens if they are
     in an alternate branch which fails to match, or if they are
     followed by # and matched zero times -- then the matched string is
     set to the empty string, and the start and end indices are set to
     -1.

     Pattern matching with backreferences is slightly slower than
     without.

B
     Deactivate backreferences, negating the effect of the b flag from
     that point on.

cN,M
     The flag (#cN,M) can be used anywhere that the # or ## operators
     can be used except in the expressions `(*/)#' and `(*/)##' in
     filename generation, where `/' has special meaning; it cannot be
     combined with other globbing flags and a bad pattern error occurs
     if it is misplaced.  It is equivalent to the form {N,M} in regular
     expressions.  The previous character or group is required to match
     between N and M times, inclusive.  The form (#cN) requires exactly
     N matches; (#c,M) is equivalent to specifying N as 0; (#cN,)
     specifies that there is no maximum limit on the number of matches.

m
     Set references to the match data for the entire string matched;
     this is similar to backreferencing and does not work in filename
     generation.  The flag must be in effect at the end of the pattern,
     i.e. not local to a group. The parameters $MATCH,  $MBEGIN and
     $MEND will be set to the string matched and to the indices of the
     beginning and end of the string, respectively.  This is most
     useful in parameter substitutions, as otherwise the string matched
     is obvious.

     For example,


          arr=(veldt jynx grimps waqf zho buck)
          print ${arr//(#m)[aeiou]/${(U)MATCH}}

     forces all the matches (i.e. all vowels) into uppercase, printing
     `vEldt jynx grImps wAqf zhO bUck'.

     Unlike backreferences, there is no speed penalty for using match
     references, other than the extra substitutions required for the
     replacement strings in cases such as the example shown.

M
     Deactivate the m flag, hence no references to match data will be
     created.

aNUM
     Approximate matching: NUM errors are allowed in the string matched
     by the pattern.  The rules for this are described in the next
     subsection.

s, e
     Unlike the other flags, these have only a local effect, and each
     must appear on its own:  `(#s)' and `(#e)' are the only valid
     forms.  The `(#s)' flag succeeds only at the start of the test
     string, and the `(#e)' flag succeeds only at the end of the test
     string; they correspond to `^' and `$' in standard regular
     expressions.  They are useful for matching path segments in
     patterns other than those in filename generation (where path
     segments are in any case treated separately).  For example,
     `*((#s)|/)test((#e)|/)*' matches a path segment `test' in any of
     the following strings: test, test/at/start, at/end/test,
     in/test/middle.

     Another use is in parameter substitution; for example
     `${array/(#s)A*Z(#e)}' will remove only elements of an array which
     match the complete pattern `A*Z'.  There are other ways of
     performing many operations of this type, however the combination
     of the substitution operations `/' and `//' with the `(#s)' and
     `(#e)' flags provides a single simple and memorable method.

     Note that assertions of the form `(^(#s))' also work, i.e. match
     anywhere except at the start of the string, although this actually
     means `anything except a zero-length portion at the start of the
     string'; you need to use `(""~(#s))' to match a zero-length
     portion of the string not at the start.

q
     A `q' and everything up to the closing parenthesis of the globbing
     flags are ignored by the pattern matching code.  This is intended
     to support the use of glob qualifiers, see below.  The result is
     that the pattern `(#b)(*).c(#q.)' can be used both for globbing
     and for matching against a string.  In the former case, the
     `(#q.)' will be treated as a glob qualifier and the `(#b)' will
     not be useful, while in the latter case the `(#b)' is useful for
     backreferences and the `(#q.)' will be ignored.  Note that colon
     modifiers in the glob qualifiers are also not applied in ordinary
     pattern matching.

u
     Respect the current locale in determining the presence of multibyte
     characters in a pattern, provided the shell was compiled with
     MULTIBYTE_SUPPORT.  This overrides the MULTIBYTE option; the
     default behaviour is taken from the option.  Compare U.
     (Mnemonic: typically multibyte characters are from Unicode in the
     UTF-8 encoding, although any extension of ASCII supported by the
     system library may be used.)

U
     All characters are considered to be a single byte long.  The
     opposite of u.  This overrides the MULTIBYTE option.


For example, the test string fooxx can be matched by the pattern
(#i)FOOXX, but not by (#l)FOOXX, (#i)FOO(#I)XX or ((#i)FOOX)X.  The
string (#ia2)readme specifies case-insensitive matching of readme with
up to two errors.

When using the ksh syntax for grouping both KSH_GLOB and EXTENDED_GLOB
must be set and the left parenthesis should be preceded by @.  Note
also that the flags do not affect letters inside [...] groups, in other
words (#i)[a-z] still matches only lowercase letters.  Finally, note
that when examining whole paths case-insensitively every directory must
be searched for all files which match, so that a pattern of the form
(#i)/foo/bar/... is potentially slow.



14.8.5 Approximate Matching
---------------------------

When matching approximately, the shell keeps a count of the errors
found, which cannot exceed the number specified in the (#aNUM) flags.
Four types of error are recognised:


1.
     Different characters, as in fooxbar and fooybar.

2.
     Transposition of characters, as in banana and abnana.

3.
     A character missing in the target string, as with the pattern road
     and target string rod.

4.
     An extra character appearing in the target string, as with stove
     and strove.


Thus, the pattern (#a3)abcd matches dcba, with the errors occurring by
using the first rule twice and the second once, grouping the string as
[d][cb][a] and [a][bc][d].

Non-literal parts of the pattern must match exactly, including
characters in character ranges: hence (#a1)???  matches strings of
length four, by applying rule 4 to an empty part of the pattern, but not
strings of length two, since all the ? must match.  Other characters
which must match exactly are initial dots in filenames (unless the
GLOB_DOTS option is set), and all slashes in filenames, so that a/bc is
two errors from ab/c (the slash cannot be transposed with another
character).  Similarly, errors are counted separately for
non-contiguous strings in the pattern, so that (ab|cd)ef is two errors
from aebf.

When using exclusion via the ~ operator, approximate matching is
treated entirely separately for the excluded part and must be activated
separately.  Thus, (#a1)README~READ_ME matches READ.ME but not READ_ME,
as the trailing READ_ME is matched without approximation.  However,
(#a1)README~(#a1)READ_ME does not match any pattern of the form READ?ME
as all such forms are now excluded.

Apart from exclusions, there is only one overall error count; however,
the maximum errors allowed may be altered locally, and this can be
delimited by grouping.  For example, (#a1)cat((#a0)dog)fox allows one
error in total, which may not occur in the dog section, and the pattern
(#a1)cat(#a0)dog(#a1)fox is equivalent.  Note that the point at which
an error is first found is the crucial one for establishing whether to
use approximation; for example, (#a1)abc(#a0)xyz will not match
abcdxyz, because the error occurs at the `x', where approximation is
turned off.

Entire path segments may be matched approximately, so that
`(#a1)/foo/d/is/available/at/the/bar' allows one error in any path
segment.  This is much less efficient than without the (#a1), however,
since every directory in the path must be scanned for a possible
approximate match.  It is best to place the (#a1) after any path
segments which are known to be correct.



14.8.6 Recursive Globbing
-------------------------

A pathname component of the form `(FOO/)#' matches a path consisting of
zero or more directories matching the pattern FOO.

As a shorthand, `**/' is equivalent to `(*/)#'; note that this
therefore matches files in the current directory as well as
subdirectories.  Thus:


     ls -ld -- (*/)#bar

or


     ls -ld -- **/bar

does a recursive directory search for files named `bar' (potentially
including the file `bar' in the current directory).  This form does not
follow symbolic links; the alternative form `***/' does, but is
otherwise identical.  Neither of these can be combined with other forms
of globbing within the same path segment; in that case, the `*'
operators revert to their usual effect.

Even shorter forms are available when the option GLOB_STAR_SHORT is
set.  In that case if no / immediately follows a ** or *** they are
treated as if both a / plus a further * are present.  Hence:


     setopt GLOBSTARSHORT
     ls -ld -- **.c

is equivalent to


     ls -ld -- **/*.c

14.8.7 Glob Qualifiers
----------------------

Patterns used for filename generation may end in a list of qualifiers
enclosed in parentheses.  The qualifiers specify which filenames that
otherwise match the given pattern will be inserted in the argument list.

If the option BARE_GLOB_QUAL is set, then a trailing set of parentheses
containing no `|' or `(' characters (or `~' if it is special) is taken
as a set of glob qualifiers.  A glob subexpression that would normally
be taken as glob qualifiers, for example `(^x)', can be forced to be
treated as part of the glob pattern by doubling the parentheses, in
this case producing `((^x))'.

If the option EXTENDED_GLOB is set, a different syntax for glob
qualifiers is available, namely `(#qX)' where X is any of the same glob
qualifiers used in the other format.  The qualifiers must still appear
at the end of the pattern.  However, with this syntax multiple glob
qualifiers may be chained together.  They are treated as a logical AND
of the individual sets of flags.  Also, as the syntax is unambiguous,
the expression will be treated as glob qualifiers just as long any
parentheses contained within it are balanced; appearance of `|', `(' or
`~' does not negate the effect.  Note that qualifiers will be
recognised in this form even if a bare glob qualifier exists at the end
of the pattern, for example `*(#q*)(.)' will recognise executable
regular files if both options are set; however, mixed syntax should
probably be avoided for the sake of clarity.  Note that within
conditions using the `[[' form the presence of a parenthesised
expression (#q...) at the end of a string indicates that globbing
should be performed; the expression may include glob qualifiers, but it
is also valid if it is simply (#q).  This does not apply to the right
hand side of pattern match operators as the syntax already has special
significance.

A qualifier may be any one of the following:


/
     directories

F
     `full' (i.e. non-empty) directories.  Note that the opposite sense
     (^F) expands to empty directories and all non-directories.  Use
     (/^F) for empty directories.

.
     plain files

@
     symbolic links

=
     sockets

p
     named pipes (FIFOs)

*
     executable plain files (0100 or 0010 or 0001)

%
     device files (character or block special)

%b
     block special files

%c
     character special files

r
     owner-readable files (0400)

w
     owner-writable files (0200)

x
     owner-executable files (0100)

A
     group-readable files (0040)

I
     group-writable files (0020)

E
     group-executable files (0010)

R
     world-readable files (0004)

W
     world-writable files (0002)

X
     world-executable files (0001)

s
     setuid files (04000)

S
     setgid files (02000)

t
     files with the sticky bit (01000)

fSPEC
     files with access rights matching SPEC. This SPEC may be a octal
     number optionally preceded by a `=', a `+', or a `-'. If none of
     these characters is given, the behavior is the same as for `='.
     The octal number describes the mode bits to be expected, if
     combined with a `=', the value given must match the file-modes
     exactly, with a `+', at least the bits in the given number must be
     set in the file-modes, and with a `-', the bits in the number must
     not be set. Giving a `?' instead of a octal digit anywhere in the
     number ensures that the corresponding bits in the file-modes are
     not checked, this is only useful in combination with `='.

     If the qualifier `f' is followed by any other character anything
     up to the next matching character (`[', `{', and `<' match `]',
     `}', and `>' respectively, any other character matches itself) is
     taken as a list of comma-separated SUB-SPECs. Each SUB-SPEC may be
     either an octal number as described above or a list of any of the
     characters `u', `g', `o', and `a', followed by a `=', a `+', or a
     `-', followed by a list of any of the characters `r', `w', `x',
     `s', and `t', or an octal digit. The first list of characters
     specify which access rights are to be checked. If a `u' is given,
     those for the owner of the file are used, if a `g' is given, those
     of the group are checked, a `o' means to test those of other
     users, and the `a' says to test all three groups. The `=', `+',
     and `-' again says how the modes are to be checked and have the
     same meaning as described for the first form above. The second
     list of characters finally says which access rights are to be
     expected: `r' for read access, `w' for write access, `x' for the
     right to execute the file (or to search a directory), `s' for the
     setuid and setgid bits, and `t' for the sticky bit.

     Thus, `*(f70?)' gives the files for which the owner has read,
     write, and execute permission, and for which other group members
     have no rights, independent of the permissions for other users.
     The pattern `*(f-100)' gives all files for which the owner does
     not have execute permission, and `*(f:gu+w,o-rx:)' gives the files
     for which the owner and the other members of the group have at
     least write permission, and for which other users don't have read
     or execute permission.

eSTRING
+CMD
     The STRING will be executed as shell code.  The filename will be
     included in the list if and only if the code returns a zero status
     (usually the status of the last command).

     In the first form, the first character after the `e' will be used
     as a separator and anything up to the next matching separator will
     be taken  as the STRING; `[', `{', and `<' match `]', `}', and
     `>', respectively, while any other character matches itself. Note
     that expansions must be quoted in the STRING to prevent them from
     being expanded before globbing is done.  STRING is then executed
     as shell code.  The string globqual is appended to the array
     zsh_eval_context the duration of execution.

     During the execution of STRING the filename currently being tested
     is available in the parameter REPLY; the parameter may be altered
     to a string to be inserted into the list instead of the original
     filename.  In addition, the parameter reply may be set to an array
     or a string, which overrides the value of REPLY.  If set to an
     array, the latter is inserted into the command line word by word.

     For example, suppose a directory contains a single file `lonely'.
     Then the expression `*(e:'reply=(${REPLY}{1,2})':)' will cause the
     words `lonely1' and `lonely2' to be inserted into the command
     line.  Note the quoting of STRING.

     The form +CMD has the same effect, but no delimiters appear around
     CMD.  Instead, CMD is taken as the longest sequence of characters
     following the + that are alphanumeric or underscore.  Typically
     CMD will be the name of a shell function that contains the
     appropriate test.  For example,


          nt() { [[ $REPLY -nt $NTREF ]] }
          NTREF=reffile
          ls -ld -- *(+nt)

     lists all files in the directory that have been modified more
     recently than reffile.

dDEV
     files on the device DEV

l[-|+]CT
     files having a link count less than CT (-), greater than CT (+),
     or equal to CT

U
     files owned by the effective user ID

G
     files owned by the effective group ID

uID
     files owned by user ID ID if that is a number.  Otherwise, ID
     specifies a user name: the character after the `u' will be taken
     as a separator and the string between it and the next matching
     separator will be taken as a user name.  The starting separators
     `[', `{', and `<' match the final separators `]', `}', and `>',
     respectively; any other character matches itself.  The selected
     files are those owned by this user.  For example, `u:foo:' or
     `u[foo]' selects files owned by user `foo'.

gID
     like uID but with group IDs or names

a[Mwhms][-|+]N
     files accessed exactly N days ago.  Files accessed within the last
     N days are selected using a negative value for N (-N).  Files
     accessed more than N days ago are selected by a positive N value
     (+N).  Optional unit specifiers `M', `w', `h', `m' or `s' (e.g.
     `ah5') cause the check to be performed with months (of 30 days),
     weeks, hours, minutes or seconds instead of days, respectively.
     An explicit `d' for days is also allowed.

     Any fractional part of the difference between the access time and
     the current part in the appropriate units is ignored in the
     comparison.  For instance, `echo *(ah-5)' would echo files
     accessed within the last five hours, while `echo *(ah+5)' would
     echo files accessed at least six hours ago, as times strictly
     between five and six hours are treated as five hours.

m[Mwhms][-|+]N
     like the file access qualifier, except that it uses the file
     modification time.

c[Mwhms][-|+]N
     like the file access qualifier, except that it uses the file inode
     change time.

L[+|-]N
     files less than N bytes (-), more than N bytes (+), or exactly N
     bytes in length.

     If this flag is directly followed by a _size specifier_ `k' (`K'),
     `m' (`M'), or `p' (`P') (e.g. `Lk-50') the check is performed with
     kilobytes, megabytes, or blocks (of 512 bytes) instead.  (On some
     systems additional specifiers are available for gigabytes, `g' or
     `G', and terabytes, `t' or `T'.) If a size specifier is used a
     file is regarded as "exactly" the size if the file size rounded up
     to the next unit is equal to the test size.  Hence `*(Lm1)'
     matches files from 1 byte up to 1 Megabyte inclusive.  Note also
     that the set of files "less than" the test size only includes
     files that would not match the equality test; hence `*(Lm-1)' only
     matches files of zero size.

^
     negates all qualifiers following it

-
     toggles between making the qualifiers work on symbolic links (the
     default) and the files they point to, if any; any symbolic link for
     whose target the `stat' system call fails (whatever the cause of
     the failure) is treated as a file in its own right

M
     sets the MARK_DIRS option for the current pattern 

T
     appends a trailing qualifier mark to the filenames, analogous to
     the LIST_TYPES option, for the current pattern (overrides M)

N
     sets the NULL_GLOB option for the current pattern 

D
     sets the GLOB_DOTS option for the current pattern 

n
     sets the NUMERIC_GLOB_SORT option for the current pattern 

YN
     enables short-circuit mode: the pattern will expand to at most N
     filenames.  If more than N matches exist, only the first N matches
     in directory traversal order will be considered.

     Implies oN when no oC qualifier is used.

oC
     specifies how the names of the files should be sorted. The
     following values of C sort in the following ways:


    n
          By name.

    L
          By the size (length) of the files.

    l
          By number of links.

    a
          By time of last access, youngest first.

    m
          By time of last modification, youngest first.

    c
          By time of last inode change, youngest first.

    d
          By directories: files in subdirectories appear before those
          in the current directory at each level of the search -- this
          is best combined with other criteria, for example `odon' to
          sort on names for files within the same directory.

    N
          No sorting is performed.

    eSTRING
    +CMD
          Sort by shell code (see below).

     Note that the modifiers ^ and - are used, so `*(^-oL)' gives a
     list of all files sorted by file size in descending order,
     following any symbolic links.  Unless oN is used, multiple order
     specifiers may occur to resolve ties.

     The default sorting is n (by name) unless the Y glob qualifier is
     used, in which case it is N (unsorted).

     oe and o+ are special cases; they are each followed by shell code,
     delimited as for the e glob qualifier and the + glob qualifier
     respectively (see above).  The code is executed for each matched
     file with the parameter REPLY set to the name of the file on entry
     and globsort appended to zsh_eval_context.  The code should modify
     the parameter REPLY in some fashion.  On return, the value of the
     parameter is used instead of the file name as the string on which
     to sort.  Unlike other sort operators, oe and o+ may be repeated,
     but note that the maximum number of sort operators of any kind
     that may appear in any glob expression is 12.

OC
     like `o', but sorts in descending order; i.e. `*(^oC)' is the same
     as `*(OC)' and `*(^OC)' is the same as `*(oC)'; `Od' puts files in
     the current directory before those in subdirectories at each level
     of the search.

[BEG[,END]]
     specifies which of the matched filenames should be included in the
     returned list. The syntax is the same as for array subscripts. BEG
     and the optional END may be mathematical expressions. As in
     parameter subscripting they may be negative to make them count
     from the last match backward. E.g.: `*(-OL[1,3])' gives a list of
     the names of the three largest files.

PSTRING
     The STRING will be prepended to each glob match as a separate
     word.  STRING is delimited in the same way as arguments to the e
     glob qualifier described above.  The qualifier can be repeated;
     the words are prepended separately so that the resulting command
     line contains the words in the same order they were given in the
     list of glob qualifiers.

     A typical use for this is to prepend an option before all
     occurrences of a file name; for example, the pattern `*(P:-f:)'
     produces the command line arguments `-f FILE1 -f FILE2 ...'

     If the modifier ^ is active, then STRING will be appended instead
     of prepended.  Prepending and appending is done independently so
     both can be used on the same glob expression; for example by
     writing `*(P:foo:^P:bar:^P:baz:)' which produces the command line
     arguments `foo baz FILE1 bar ...'


More than one of these lists can be combined, separated by commas. The
whole list matches if at least one of the sublists matches (they are
`or'ed, the qualifiers in the sublists are `and'ed).  Some qualifiers,
however, affect all matches generated, independent of the sublist in
which they are given.  These are the qualifiers `M', `T', `N', `D',
`n', `o', `O' and the subscripts given in brackets (`[...]').

If a `:' appears in a qualifier list, the remainder of the expression in
parenthesis is interpreted as a modifier (see *Note Modifiers:: in
*Note History Expansion::).  Each modifier must be introduced by a
separate `:'.  Note also that the result after modification does not
have to be an existing file.  The name of any existing file can be
followed by a modifier of the form `(:...)'  even if no actual filename
generation is performed, although note that the presence of the
parentheses causes the entire expression to be subjected to any global
pattern matching options such as NULL_GLOB. Thus:


     ls -ld -- *(-/)

lists all directories and symbolic links that point to directories, and


     ls -ld -- *(-@)

lists all broken symbolic links, and


     ls -ld -- *(%W)

lists all world-writable device files in the current directory, and


     ls -ld -- *(W,X)

lists all files in the current directory that are world-writable or
world-executable, and


     print -rC1 /tmp/foo*(u0^@:t)

outputs the basename of all root-owned files beginning with the string
`foo' in /tmp, ignoring symlinks, and


     ls -ld -- *.*~(lex|parse).[ch](^D^l1)

lists all files having a link count of one whose names contain a dot
(but not those starting with a dot, since GLOB_DOTS is explicitly
switched off) except for lex.c, lex.h, parse.c and parse.h.


     print -rC1 b*.pro(#q:s/pro/shmo/)(#q.:s/builtin/shmiltin/)

demonstrates how colon modifiers and other qualifiers may be chained
together.  The ordinary qualifier `.' is applied first, then the colon
modifiers in order from left to right.  So if EXTENDED_GLOB is set and
the base pattern matches the regular file builtin.pro, the shell will
print `shmiltin.shmo'.


File: zsh.info,  Node: Parameters,  Next: Options,  Prev: Expansion,  Up: Top

15 Parameters
*************



15.1 Description
================

A parameter has a name, a value, and a number of attributes.  A name
may be any sequence of alphanumeric characters and underscores, or the
single characters `*', `@', `#', `?', `-', `$', or `!'.  A parameter
whose name begins with an alphanumeric or underscore is also referred
to as a _variable_.

The attributes of a parameter determine the _type_ of its value, often
referred to as the parameter type or variable type, and also control
other processing that may be applied to the value when it is referenced.
The value type may be a _scalar_ (a string, an integer, or a floating
point number), an array (indexed numerically), or an _associative_
array (an unordered set of name-value pairs, indexed by name, also
referred to as a _hash_).

Named scalar parameters may have the _exported_, -x, attribute, to copy
them into the process environment, which is then passed from the shell
to any new processes that it starts.  Exported parameters are called
_environment variables_. The shell also _imports_ environment variables
at startup time and automatically marks the corresponding parameters as
exported.  Some environment variables are not imported for reasons of
security or because they would interfere with the correct operation of
other shell features.

Parameters may also be _special_, that is, they have a predetermined
meaning to the shell.  Special parameters cannot have their type changed
or their readonly attribute turned off, and if a special parameter is
unset, then later recreated, the special properties will be retained.

To declare the type of a parameter, or to assign a string or numeric
value to a scalar parameter, use the typeset builtin.  

The value of a scalar parameter may also be assigned by writing: 

     NAME=VALUE

In scalar assignment, VALUE is expanded as a single string, in which
the elements of arrays are joined together; filename expansion is not
performed unless the option GLOB_ASSIGN is set.

When the integer attribute, -i, or a floating point attribute, -E or
-F, is set for NAME, the VALUE is subject to arithmetic evaluation.
Furthermore, by replacing `=' with `+=', a parameter can be incremented
or appended to.  See *Note Array Parameters:: and *Note Arithmetic
Evaluation:: for additional forms of assignment.

Note that assignment may implicitly change the attributes of a
parameter.  For example, assigning a number to a variable in arithmetic
evaluation may change its type to integer or float, and with
GLOB_ASSIGN assigning a pattern to a variable may change its type to an
array.

To reference the value of a parameter, write `$NAME' or `${NAME}'.  See
*Note Parameter Expansion:: for complete details.  That section also
explains the effect of the difference between scalar and array
assignment on parameter expansion.

* Menu:

* Array Parameters::
* Positional Parameters::
* Local Parameters::
* Parameters Set By The Shell::
* Parameters Used By The Shell::


File: zsh.info,  Node: Array Parameters,  Next: Positional Parameters,  Up: Parameters

15.2 Array Parameters
=====================

To assign an array value, write one of: 

     set -A NAME VALUE ...

     NAME=(VALUE ...)

     NAME=([KEY]=VALUE ...)

If no parameter NAME exists, an ordinary array parameter is created.
If the parameter NAME exists and is a scalar, it is replaced by a new
array.

In the third form, KEY is an expression that will be evaluated in
arithmetic context (in its simplest form, an integer) that gives the
index of the element to be assigned with VALUE.  In this form any
elements not explicitly mentioned that come before the largest index to
which a value is assigned are assigned an empty string.  The indices
may be in any order.  Note that this syntax is strict: [ and ]= must
not be quoted, and KEY may not consist of the unquoted string ]=, but
is otherwise treated as a simple string.  The enhanced forms of
subscript expression that may be used when directly subscripting a
variable name, described in the section `Array Subscripts' below, are
not available.

The syntaxes with and without the explicit key may be mixed.  An
implicit KEY is deduced by incrementing the index from the previously
assigned element.  Note that it is not treated as an error if latter
assignments in this form overwrite earlier assignments.

For example, assuming the option KSH_ARRAYS is not set, the following:


     array=(one [3]=three four)

causes the array variable array to contain four elements one, an empty
string, three and four, in that order.

In the forms where only VALUE is specified, full command line expansion
is performed.

In the [KEY]=VALUE form, both KEY and VALUE undergo all forms of
expansion allowed for single word shell expansions (this does not
include filename generation); these are as performed by the parameter
expansion flag (e) as described in *Note Parameter Expansion::.  Nested
parentheses may surround VALUE and are included as part of the value,
which is joined into a plain string; this differs from ksh which allows
the values themselves to be arrays.  A future version of zsh may
support that.  To cause the brackets to be interpreted as a character
class for filename generation, and therefore to treat the resulting list
of files as a set of values, quote the equal sign using any form of
quoting.  Example:

     NAME=([a-z]'='*)

To append to an array without changing the existing values, use one of
the following:

     NAME+=(VALUE ...)

     NAME+=([KEY]=VALUE ...)

In the second form KEY may specify an existing index as well as an
index off the end of the old array; any existing value is overwritten by
VALUE.  Also, it is possible to use [KEY]+=VALUE to append to the
existing value at that index.

Within the parentheses on the right hand side of either form of the
assignment, newlines and semicolons are treated the same as white space,
separating individual VALUEs.  Any consecutive sequence of such
characters has the same effect.

Ordinary array parameters may also be explicitly declared with: 

     typeset -a NAME

Associative arrays _must_ be declared before assignment, by using:

     typeset -A NAME

When NAME refers to an associative array, the list in an assignment is
interpreted as alternating keys and values:

     set -A NAME KEY VALUE ...

     NAME=(KEY VALUE ...)

     NAME=([KEY]=VALUE ...)

Note that only one of the two syntaxes above may be used in any given
assignment; the forms may not be mixed.  This is unlike the case of
numerically indexed arrays.

Every KEY must have a VALUE in this case.  Note that this assigns to
the entire array, deleting any elements that do not appear in the list.
The append syntax may also be used with an associative array:

     NAME+=(KEY VALUE ...)

     NAME+=([KEY]=VALUE ...)

This adds a new key/value pair if the key is not already present, and
replaces the value for the existing key if it is.  In the second form
it is also possible to use [KEY]+=VALUE to append to the existing value
at that key.  Expansion is performed identically to the corresponding
forms for normal arrays, as described above.

To create an empty array (including associative arrays), use one of:

     set -A NAME

     NAME=()


15.2.1 Array Subscripts
-----------------------

Individual elements of an array may be selected using a subscript.  A
subscript of the form `[EXP]' selects the single element EXP, where EXP
is an arithmetic expression which will be subject to arithmetic
expansion as if it were surrounded by `$((...))'.  The elements are
numbered beginning with 1, unless the KSH_ARRAYS option is set in which
case they are numbered from zero.  

Subscripts may be used inside braces used to delimit a parameter name,
thus `${foo[2]}' is equivalent to `$foo[2]'.  If the KSH_ARRAYS option
is set, the braced form is the only one that works, as bracketed
expressions otherwise are not treated as subscripts.

If the KSH_ARRAYS option is not set, then by default accesses to an
array element with a subscript that evaluates to zero return an empty
string, while an attempt to write such an element is treated as an
error.  For backward compatibility the KSH_ZERO_SUBSCRIPT option can be
set to cause subscript values 0 and 1 to be equivalent; see the
description of the option in *Note Description of Options::.

The same subscripting syntax is used for associative arrays, except that
no arithmetic expansion is applied to EXP.  However, the parsing rules
for arithmetic expressions still apply, which affects the way that
certain special characters must be protected from interpretation.  See
_Subscript Parsing_ below for details.

A subscript of the form `[*]' or `[@]' evaluates to all elements of an
array; there is no difference between the two except when they appear
within double quotes.  `"$foo[*]"' evaluates to `"$foo[1] $foo[2]
..."', whereas `"$foo[@]"' evaluates to `"$foo[1]" "$foo[2]" ...'.  For
associative arrays, `[*]' or `[@]' evaluate to all the values, in no
particular order.  Note that this does not substitute the keys; see the
documentation for the `k' flag under *Note Parameter Expansion:: for
complete details.  When an array parameter is referenced as `$NAME'
(with no subscript) it evaluates to `$NAME[*]', unless the KSH_ARRAYS
option is set in which case it evaluates to `${NAME[0]}' (for an
associative array, this means the value of the key `0', which may not
exist even if there are values for other keys).

A subscript of the form `[EXP1,EXP2]' selects all elements in the range
EXP1 to EXP2, inclusive. (Associative arrays are unordered, and so do
not support ranges.) If one of the subscripts evaluates to a negative
number, say -N, then the Nth element from the end of the array is used.
Thus `$foo[-3]' is the third element from the end of the array foo, and
`$foo[1,-1]' is the same as `$foo[*]'.

Subscripting may also be performed on non-array values, in which case
the subscripts specify a substring to be extracted.  For example, if
FOO is set to `foobar', then `echo $FOO[2,5]' prints `ooba'.  Note that
some forms of subscripting described below perform pattern matching,
and in that case the substring extends from the start of the match of
the first subscript to the end of the match of the second subscript.
For example,


     string="abcdefghijklm"
     print ${string[(r)d?,(r)h?]}

prints `defghi'.  This is an obvious generalisation of the rule for
single-character matches.  For a single subscript, only a single
character is referenced (not the range of characters covered by the
match).

Note that in substring operations the second subscript is handled
differently by the r and R subscript flags: the former takes the
shortest match as the length and the latter the longest match.  Hence
in the former case a * at the end is redundant while in the latter case
it matches the whole remainder of the string.  This does not affect the
result of the single subscript case as here the length of the match is
irrelevant.



15.2.2 Array Element Assignment
-------------------------------

A subscript may be used on the left side of an assignment like so:

     NAME[EXP]=VALUE

In this form of assignment the element or range specified by EXP is
replaced by the expression on the right side.  An array (but not an
associative array) may be created by assignment to a range or element.
Arrays do not nest, so assigning a parenthesized list of values to an
element or range changes the number of elements in the array, shifting
the other elements to accommodate the new values.  (This is not
supported for associative arrays.)

This syntax also works as an argument to the typeset command:

     typeset "NAME[EXP]"=VALUE

The VALUE may _not_ be a parenthesized list in this case; only
single-element assignments may be made with typeset.  Note that quotes
are necessary in this case to prevent the brackets from being
interpreted as filename generation operators.  The noglob precommand
modifier could be used instead.

To delete an element of an ordinary array, assign `()' to that element.
To delete an element of an associative array, use the unset command:

     unset "NAME[EXP]"


15.2.3 Subscript Flags
----------------------

If the opening bracket, or the comma in a range, in any subscript
expression is directly followed by an opening parenthesis, the string up
to the matching closing one is considered to be a list of flags, as in
`NAME[(FLAGS)EXP]'.

The flags s, n and b take an argument; the delimiter is shown below as
`:', but any character, or the matching pairs `(...)', `{...}',
`[...]', or `<...>', may be used, but note that `<...>' can only be
used if the subscript is inside a double quoted expression or a
parameter substitution enclosed in braces as otherwise the expression is
interpreted as a redirection.

The flags currently understood are:


w
     If the parameter subscripted is a scalar then this flag makes
     subscripting work on words instead of characters.  The default word
     separator is whitespace.  When combined with the i or I flag, the
     effect is to produce the index of the first character of the
     first/last word which matches the given pattern; note that a failed
     match in this case always yields 0.

s:STRING:
     This gives the STRING that separates words (for use with the w
     flag).  The delimiter character : is arbitrary; see above.

p
     Recognize the same escape sequences as the print builtin in the
     string argument of a subsequent `s' flag.

f
     If the parameter subscripted is a scalar then this flag makes
     subscripting work on lines instead of characters, i.e. with
     elements separated by newlines.  This is a shorthand for `pws:\n:'.

r
     Reverse subscripting: if this flag is given, the EXP is taken as a
     pattern and the result is the first matching array element,
     substring or word (if the parameter is an array, if it is a
     scalar, or if it is a scalar and the `w' flag is given,
     respectively).  The subscript used is the number of the matching
     element, so that pairs of subscripts such as `$foo[(r)??,3]' and
     `$foo[(r)??,(r)f*]' are possible if the parameter is not an
     associative array.  If the parameter is an associative array, only
     the value part of each pair is compared to the pattern, and the
     result is that value.

     If a search through an ordinary array failed, the search sets the
     subscript to one past the end of the array, and hence
     ${array[(r)PATTERN]} will substitute the empty string.  Thus the
     success of a search can be tested by using the (i) flag, for
     example (assuming the option KSH_ARRAYS is not in effect):


          [[ ${array[(i)pattern]} -le ${#array} ]]

     If KSH_ARRAYS is in effect, the -le should be replaced by -lt.

R
     Like `r', but gives the last match.  For associative arrays, gives
     all possible matches. May be used for assigning to ordinary array
     elements, but not for assigning to associative arrays.  On
     failure, for normal arrays this has the effect of returning the
     element corresponding to subscript 0; this is empty unless one of
     the options KSH_ARRAYS or KSH_ZERO_SUBSCRIPT is in effect.

     Note that in subscripts with both `r' and `R' pattern characters
     are active even if they were substituted for a parameter
     (regardless of the setting of GLOB_SUBST which controls this
     feature in normal pattern matching).  The flag `e' can be added to
     inhibit pattern matching.  As this flag does not inhibit other
     forms of substitution, care is still required; using a parameter
     to hold the key has the desired effect:


          key2='original key'
          print ${array[(Re)$key2]}

i
     Like `r', but gives the index of the match instead; this may not be
     combined with a second argument.  On the left side of an
     assignment, behaves like `r'.  For associative arrays, the key
     part of each pair is compared to the pattern, and the first
     matching key found is the result.  On failure substitutes the
     length of the array plus one, as discussed under the description
     of `r', or the empty string for an associative array.

     Note: Although `i' may be applied to a scalar substitution to find
     the offset of a substring, the results are likely to be misleading
     when searching within substitutions that yield an empty string, or
     when searching for the empty substring.

I
     Like `i', but gives the index of the last match, or all possible
     matching keys in an associative array.  On failure substitutes 0,
     or the empty string for an associative array.  This flag is best
     when testing for values or keys that do not exist.

     Note: If the option KSH_ARRAYS is in effect and no match is found,
     the result is indistinguishable from the case when the first
     element of the array matches.

k
     If used in a subscript on an associative array, this flag causes
     the keys to be interpreted as patterns, and returns the value for
     the first key found where EXP is matched by the key.  Note this
     could be any such key as no ordering of associative arrays is
     defined.  This flag does not work on the left side of an
     assignment to an associative array element.  If used on another
     type of parameter, this behaves like `r'.

K
     On an associative array this is like `k' but returns all values
     where EXP is matched by the keys.  On other types of parameters
     this has the same effect as `R'.

n:EXPR:
     If combined with `r', `R', `i' or `I', makes them give the Nth or
     Nth last match (if EXPR evaluates to N).  This flag is ignored
     when the array is associative.  The delimiter character : is
     arbitrary; see above.

b:EXPR:
     If combined with `r', `R', `i' or `I', makes them begin at the Nth
     or Nth last element, word, or character (if EXPR evaluates to N).
     This flag is ignored when the array is associative.  The delimiter
     character : is arbitrary; see above.

e
     This flag causes any pattern matching that would be performed on
     the subscript to use plain string matching instead.  Hence
     `${array[(re)*]}' matches only the array element whose value is *.
     Note that other forms of substitution such as parameter
     substitution are not inhibited.

     This flag can also be used to force * or @ to be interpreted as a
     single key rather than as a reference to all values.  It may be
     used for either purpose on the left side of an assignment.


See _Parameter Expansion Flags_ (*Note Parameter Expansion::) for
additional ways to manipulate the results of array subscripting.



15.2.4 Subscript Parsing
------------------------

This discussion applies mainly to associative array key strings and to
patterns used for reverse subscripting (the `r', `R', `i', etc. flags),
but it may also affect parameter substitutions that appear as part of
an arithmetic expression in an ordinary subscript.

To avoid subscript parsing limitations in assignments to associative
array elements, use the append syntax:


     aa+=('key with "*strange*" characters' 'value string')

The basic rule to remember when writing a subscript expression is that
all text between the opening `[' and the closing `]' is interpreted _as
if_ it were in double quotes (*Note Quoting::).  However, unlike double
quotes which normally cannot nest, subscript expressions may appear
inside double-quoted strings or inside other subscript expressions (or
both!), so the rules have two important differences.

The first difference is that brackets (`[' and `]') must appear as
balanced pairs in a subscript expression unless they are preceded by a
backslash (`\').  Therefore, within a subscript expression (and unlike
true double-quoting) the sequence `\[' becomes `[', and similarly `\]'
becomes `]'.  This applies even in cases where a backslash is not
normally required; for example, the pattern `[^[]' (to match any
character other than an open bracket) should be written `[^\[]' in a
reverse-subscript pattern.  However, note that `\[^\[\]' and even
`\[^[]' mean the _same_ thing, because backslashes are always stripped
when they appear before brackets!

The same rule applies to parentheses (`(' and `)') and braces (`{' and
`}'): they must appear either in balanced pairs or preceded by a
backslash, and backslashes that protect parentheses or braces are
removed during parsing.  This is because parameter expansions may be
surrounded by balanced braces, and subscript flags are introduced by
balanced parentheses.

The second difference is that a double-quote (`"') may appear as part
of a subscript expression without being preceded by a backslash, and
therefore that the two characters `\"' remain as two characters in the
subscript (in true double-quoting, `\"' becomes `"').  However, because
of the standard shell quoting rules, any double-quotes that appear must
occur in balanced pairs unless preceded by a backslash.  This makes it
more difficult to write a subscript expression that contains an odd
number of double-quote characters, but the reason for this difference is
so that when a subscript expression appears inside true double-quotes,
one can still write `\"' (rather than `\\\"') for `"'.

To use an odd number of double quotes as a key in an assignment, use the
typeset builtin and an enclosing pair of double quotes; to refer to the
value of that key, again use double quotes:


     typeset -A aa
     typeset "aa[one\"two\"three\"quotes]"=QQQ
     print "$aa[one\"two\"three\"quotes]"

It is important to note that the quoting rules do not change when a
parameter expansion with a subscript is nested inside another subscript
expression.  That is, it is not necessary to use additional backslashes
within the inner subscript expression; they are removed only once, from
the innermost subscript outwards.  Parameters are also expanded from the
innermost subscript first, as each expansion is encountered left to
right in the outer expression.

A further complication arises from a way in which subscript parsing is
_not_ different from double quote parsing.  As in true double-quoting,
the sequences `\*', and `\@' remain as two characters when they appear
in a subscript expression.  To use a literal `*' or `@' as an
associative array key, the `e' flag must be used:


     typeset -A aa
     aa[(e)*]=star
     print $aa[(e)*]

A last detail must be considered when reverse subscripting is performed.
Parameters appearing in the subscript expression are first expanded and
then the complete expression is interpreted as a pattern.  This has two
effects: first, parameters behave as if GLOB_SUBST were on (and it
cannot be turned off); second, backslashes are interpreted twice, once
when parsing the array subscript and again when parsing the pattern.
In a reverse subscript, it's necessary to use _four_ backslashes to
cause a single backslash to match literally in the pattern.  For
complex patterns, it is often easiest to assign the desired pattern to
a parameter and then refer to that parameter in the subscript, because
then the backslashes, brackets, parentheses, etc., are seen only when
the complete expression is converted to a pattern.  To match the value
of a parameter literally in a reverse subscript, rather than as a
pattern, use `${(q)NAME}' (*Note Parameter Expansion::) to quote the
expanded value.

Note that the `k' and `K' flags are reverse subscripting for an
ordinary array, but are _not_ reverse subscripting for an associative
array!  (For an associative array, the keys in the array itself are
interpreted as patterns by those flags; the subscript is a plain string
in that case.)

One final note, not directly related to subscripting: the numeric names
of positional parameters (*Note Positional Parameters::) are parsed
specially, so for example `$2foo' is equivalent to `${2}foo'.
Therefore, to use subscript syntax to extract a substring from a
positional parameter, the expansion must be surrounded by braces; for
example, `${2[3,5]}' evaluates to the third through fifth characters of
the second positional parameter, but `$2[3,5]' is the entire second
parameter concatenated with the filename generation pattern `[3,5]'.




File: zsh.info,  Node: Positional Parameters,  Next: Local Parameters,  Prev: Array Parameters,  Up: Parameters

15.3 Positional Parameters
==========================

The positional parameters provide access to the command-line arguments
of a shell function, shell script, or the shell itself; see *Note
Invocation::, and also *Note Functions::.  The parameter N, where N is
a number, is the Nth positional parameter.  The parameter `$0' is a
special case, see *Note Parameters Set By The Shell::.

The parameters *, @ and argv are arrays containing all the positional
parameters; thus `$argv[N]', etc., is equivalent to simply `$N'.  Note
that the options KSH_ARRAYS or KSH_ZERO_SUBSCRIPT apply to these arrays
as well, so with either of those options set, `${argv[0]}' is
equivalent to `$1' and so on.

Positional parameters may be changed after the shell or function starts
by using the set builtin, by assigning to the argv array, or by direct
assignment of the form `N=VALUE' where N is the number of the
positional parameter to be changed.  This also creates (with empty
values) any of the positions from 1 to N that do not already have
values.  Note that, because the positional parameters form an array, an
array assignment of the form `N=(VALUE ...)' is allowed, and has the
effect of shifting all the values at positions greater than N by as
many positions as necessary to accommodate the new values.




File: zsh.info,  Node: Local Parameters,  Next: Parameters Set By The Shell,  Prev: Positional Parameters,  Up: Parameters

15.4 Local Parameters
=====================

Shell function executions delimit scopes for shell parameters.
(Parameters are dynamically scoped.)  The typeset builtin, and its
alternative forms declare, integer, local and readonly (but not
export), can be used to declare a parameter as being local to the
innermost scope.

When a parameter is read or assigned to, the innermost existing
parameter of that name is used.  (That is, the local parameter hides
any less-local parameter.)  However, assigning to a non-existent
parameter, or declaring a new parameter with export, causes it to be
created in the _outer_most scope.

Local parameters disappear when their scope ends.  unset can be used to
delete a parameter while it is still in scope; any outer parameter of
the same name remains hidden.

Special parameters may also be made local; they retain their special
attributes unless either the existing or the newly-created parameter
has the -h (hide) attribute.  This may have unexpected effects: there
is no default value, so if there is no assignment at the point the
variable is made local, it will be set to an empty value (or zero in
the case of integers).  The following:


     typeset PATH=/new/directory:$PATH

is valid for temporarily allowing the shell or programmes called from
it to find the programs in /new/directory inside a function.

Note that the restriction in older versions of zsh that local parameters
were never exported has been removed.




File: zsh.info,  Node: Parameters Set By The Shell,  Next: Parameters Used By The Shell,  Prev: Local Parameters,  Up: Parameters

15.5 Parameters Set By The Shell
================================

In the parameter lists that follow, the mark `<S>' indicates that the
parameter is special.  `<Z>' indicates that the parameter does not exist
when the shell initializes in sh or ksh emulation mode.

The parameters `!', `#', `*', `-', `?', `@', `$', `ARGC', `HISTCMD',
`LINENO', `PPID', `status', `TTYIDLE', `zsh_eval_context',
`ZSH_EVAL_CONTEXT', and `ZSH_SUBSHELL' are read-only and thus cannot be
restored by the user, so they are not output by `typeset -p'.  This
also applies to many read-only parameters loaded from modules.

The following parameters are automatically set by the shell:


! <S>
     The process ID of the last command started in the background with
     &, put into the background with the bg builtin, or spawned with
     coproc.

# <S>
     The number of positional parameters in decimal.  Note that some
     confusion may occur with the syntax $#PARAM which substitutes the
     length of PARAM.  Use ${#} to resolve ambiguities.  In particular,
     the sequence `$#-...' in an arithmetic expression is interpreted as
     the length of the parameter -, q.v.

ARGC <S> <Z>
     Same as #.

$ <S>
     The process ID of this shell, set when the shell initializes.
     Processes forked from the shell without executing a new program,
     such as command substitutions and commands grouped with (...), are
     subshells that duplicate the current shell, and thus substitute the
     same value for $$ as their parent shell.

- <S>
     Flags supplied to the shell on invocation or by the set or setopt
     commands.

* <S>
     An array containing the positional parameters.

argv <S> <Z>
     Same as *.  Assigning to argv changes the local positional
     parameters, but argv is _not_ itself a local parameter.  Deleting
     argv with unset in any function deletes it everywhere, although
     only the innermost positional parameter array is deleted (so * and
     @ in other scopes are not affected).

@ <S>
     Same as argv[@], even when argv is not set.

? <S>
     The exit status returned by the last command.

0 <S>
     The name used to invoke the current shell, or as set by the -c
     command line option upon invocation.  If the FUNCTION_ARGZERO
     option is set, $0 is set upon entry to a shell function to the
     name of the function, and upon entry to a sourced script to the
     name of the script, and reset to its previous value when the
     function or script returns.

status <S> <Z>
     Same as ?.

pipestatus <S> <Z>
     An array containing the exit statuses returned by all commands in
     the last pipeline.

_ <S>
     The last argument of the previous command.  Also, this parameter
     is set in the environment of every command executed to the full
     pathname of the command.

CPUTYPE
     The machine type (microprocessor class or machine model), as
     determined at run time.

EGID <S>
     The effective group ID of the shell process.  If you have
     sufficient privileges, you may change the effective group ID of
     the shell process by assigning to this parameter.  Also (assuming
     sufficient privileges), you may start a single command with a
     different effective group ID by `(EGID=GID; command)'

     If this is made local, it is not implicitly set to 0, but may be
     explicitly set locally.

EUID <S>
     The effective user ID of the shell process.  If you have sufficient
     privileges, you may change the effective user ID of the shell
     process by assigning to this parameter.  Also (assuming sufficient
     privileges), you may start a single command with a different
     effective user ID by `(EUID=UID; command)'

     If this is made local, it is not implicitly set to 0, but may be
     explicitly set locally.

ERRNO <S>
     The value of errno (see errno(3)) as set by the most recently
     failed system call.  This value is system dependent and is
     intended for debugging purposes.  It is also useful with the
     zsh/system module which allows the number to be turned into a name
     or message.

     To use this parameter, it must first be assigned a value (typically
     0 (zero)).  It is initially unset for scripting compatibility.

FUNCNEST <S>
     Integer.  If greater than or equal to zero, the maximum nesting
     depth of shell functions.  When it is exceeded, an error is raised
     at the point where a function is called.  The default value is
     determined when the shell is configured, but is typically 500.
     Increasing the value increases the danger of a runaway function
     recursion causing the shell to crash.  Setting a negative value
     turns off the check.

GID <S>
     The real group ID of the shell process.  If you have sufficient
     privileges, you may change the group ID of the shell process by
     assigning to this parameter.  Also (assuming sufficient
     privileges), you may start a single command under a different
     group ID by `(GID=GID; command)'

     If this is made local, it is not implicitly set to 0, but may be
     explicitly set locally.

HISTCMD
     The current history event number in an interactive shell, in other
     words the event number for the command that caused $HISTCMD to be
     read.  If the current history event modifies the history, HISTCMD
     changes to the new maximum history event number.

HOST
     The current hostname.

LINENO <S>
     The line number of the current line within the current script,
     sourced file, or shell function being executed, whichever was
     started most recently.  Note that in the case of shell functions
     the line number refers to the function as it appeared in the
     original definition, not necessarily as displayed by the functions
     builtin.

LOGNAME
     If the corresponding variable is not set in the environment of the
     shell, it is initialized to the login name corresponding to the
     current login session. This parameter is exported by default but
     this can be disabled using the typeset builtin.  The value is set
     to the string returned by the getlogin(3) system call if that is
     available.

MACHTYPE
     The machine type (microprocessor class or machine model), as
     determined at compile time.

OLDPWD
     The previous working directory.  This is set when the shell
     initializes and whenever the directory changes.

OPTARG <S>
     The value of the last option argument processed by the getopts
     command.

OPTIND <S>
     The index of the last option argument processed by the getopts
     command.

OSTYPE
     The operating system, as determined at compile time.

PPID <S>
     The process ID of the parent of the shell, set when the shell
     initializes.  As with $$, the value does not change in subshells
     created as a duplicate of the current shell.

PWD
     The present working directory.  This is set when the shell
     initializes and whenever the directory changes.

RANDOM <S>
     A pseudo-random integer from 0 to 32767, newly generated each time
     this parameter is referenced.  The random number generator can be
     seeded by assigning a numeric value to RANDOM.

     The values of RANDOM form an intentionally-repeatable pseudo-random
     sequence; subshells that reference RANDOM will result in identical
     pseudo-random values unless the value of RANDOM is referenced or
     seeded in the parent shell in between subshell invocations.

SECONDS <S>
     The number of seconds since shell invocation.  If this parameter
     is assigned a value, then the value returned upon reference will
     be the value that was assigned plus the number of seconds since
     the assignment.

     Unlike other special parameters, the type of the SECONDS parameter
     can be changed using the typeset command.  The type may be changed
     only to one of the floating point types or back to integer.  For
     example, `typeset -F SECONDS' causes the value to be reported as a
     floating point number.  The value is available to microsecond
     accuracy, although the shell may show more or fewer digits
     depending on the use of typeset.  See the documentation for the
     builtin typeset in *Note Shell Builtin Commands:: for more details.

SHLVL <S>
     Incremented by one each time a new shell is started.

signals
     An array containing the names of the signals.  Note that with the
     standard zsh numbering of array indices, where the first element
     has index 1, the signals are offset by 1 from the signal number
     used by the operating system.  For example, on typical Unix-like
     systems HUP is signal number 1, but is referred to as $signals[2].
     This is because of EXIT at position 1 in the array, which is used
     internally by zsh but is not known to the operating system. On
     many systems there is a block of reserved or unused signal numbers
     before the POSIX real-time signals so the array index can't be
     used as an accurate indicator of their signal number. Use, for
     example, kill -l SIGRTMIN instead.

TRY_BLOCK_ERROR <S>
     In an always block, indicates whether the preceding list of code
     caused an error.  The value is 1 to indicate an error, 0 otherwise.
     It may be reset, clearing the error condition.  See *Note Complex
     Commands::

TRY_BLOCK_INTERRUPT <S>
     This variable works in a similar way to TRY_BLOCK_ERROR, but
     represents the status of an interrupt from the signal SIGINT, which
     typically comes from the keyboard when the user types ^C.  If set
     to 0, any such interrupt will be reset; otherwise, the interrupt is
     propagated after the always block.

     Note that it is possible that an interrupt arrives during the
     execution of the always block; this interrupt is also propagated.

TTY
     The name of the tty associated with the shell, if any.

TTYIDLE <S>
     The idle time of the tty associated with the shell in seconds or
     -1 if there is no such tty.

UID <S>
     The real user ID of the shell process.  If you have sufficient
     privileges, you may change the user ID of the shell by assigning
     to this parameter.  Also (assuming sufficient privileges), you may
     start a single command under a different user ID by `(UID=UID;
     command)'

     If this is made local, it is not implicitly set to 0, but may be
     explicitly set locally.

USERNAME <S>
     The username corresponding to the real user ID of the shell
     process.  If you have sufficient privileges, you may change the
     username (and also the user ID and group ID) of the shell by
     assigning to this parameter.  Also (assuming sufficient
     privileges), you may start a single command under a different
     username (and user ID and group ID) by `(USERNAME=USERNAME;
     command)'

VENDOR
     The vendor, as determined at compile time.

zsh_eval_context <S> <Z> (ZSH_EVAL_CONTEXT <S>)
     An array (colon-separated list) indicating the context of shell
     code that is being run.  Each time a piece of shell code that is
     stored within the shell is executed a string is temporarily
     appended to the array to indicate the type of operation that is
     being performed.  Read in order the array gives an indication of
     the stack of operations being performed with the most immediate
     context last.

     Note that the variable does not give information on syntactic
     context such as pipelines or subshells.  Use $ZSH_SUBSHELL to
     detect subshells.

     The context is one of the following:
    cmdarg
          Code specified by the -c option to the command line that
          invoked the shell.

    cmdsubst
          Command substitution using the `...` or $(...) construct.

    equalsubst
          File substitution using the =(...) construct.

    eval
          Code executed by the eval builtin.

    evalautofunc
          Code executed with the KSH_AUTOLOAD mechanism in order to
          define an autoloaded function.

    fc
          Code from the shell history executed by the -e option to the
          fc builtin.

    file
          Lines of code being read directly from a file, for example by
          the source builtin.

    filecode
          Lines of code being read from a .zwc file instead of directly
          from the source file.

    globqual
          Code executed by the e or + glob qualifier.

    globsort
          Code executed to order files by the o glob qualifier.

    insubst
          File substitution using the <(...) construct.

    loadautofunc
          Code read directly from a file to define an autoloaded
          function.

    outsubst
          File substitution using the >(...) construct.

    sched
          Code executed by the sched builtin.

    shfunc
          A shell function.

    stty
          Code passed to stty by the STTY environment variable.
          Normally this is passed directly to the system's stty command,
          so this value is unlikely to be seen in practice.

    style
          Code executed as part of a style retrieved by the zstyle
          builtin from the zsh/zutil module.

    toplevel
          The highest execution level of a script or interactive shell.

    trap
          Code executed as a trap defined by the trap builtin.  Traps
          defined as functions have the context shfunc.  As traps are
          asynchronous they may have a different hierarchy from other
          code.

    zpty
          Code executed by the zpty builtin from the zsh/zpty module.

    zregexparse-guard
          Code executed as a guard by the zregexparse command from the
          zsh/zutil module.

    zregexparse-action
          Code executed as an action by the zregexparse command from the
          zsh/zutil module.


ZSH_ARGZERO
     If zsh was invoked to run a script, this is the name of the script.
     Otherwise, it is the name used to invoke the current shell.  This
     is the same as the value of $0 when the POSIX_ARGZERO option is
     set, but is always available.

ZSH_EXECUTION_STRING
     If the shell was started with the option -c, this contains the
     argument passed to the option.  Otherwise it is not set.

ZSH_NAME
     Expands to the basename of the command used to invoke this instance
     of zsh.

ZSH_PATCHLEVEL
     The output of `git describe -tags -long' for the zsh repository
     used to build the shell.  This is most useful in order to keep
     track of versions of the shell during development between releases;
     hence most users should not use it and should instead rely on
     $ZSH_VERSION.

zsh_scheduled_events
     See *Note The zsh/sched Module::.

ZSH_SCRIPT
     If zsh was invoked to run a script, this is the name of the script,
     otherwise it is unset.

ZSH_SUBSHELL
     Readonly integer.  Initially zero, incremented each time the shell
     forks to create a subshell for executing code.  Hence `(print
     $ZSH_SUBSHELL)' and `print $(print $ZSH_SUBSHELL)' output 1, while
     `( (print $ZSH_SUBSHELL) )' outputs 2.

ZSH_VERSION
     The version number of the release of zsh.


