#!/usr/pkg/bin/perl

use File::Basename;
use Getopt::Long;

use constant MSWIN => $^O =~ /MSWin32|Windows_NT/i ? 1 : 0;

sub usage {
    my $msg = shift;
    my $rc = (defined($msg) && !$msg) ? 0 : 2;
    if ($rc) {
	select STDERR;
	print $msg if $msg && $msg =~ /^\d+$/;
    }
    my $prog = basename($0, qw(.pl));
    print <<EOF;
Usage: $prog [VAR=TOKEN,TOKEN,...] ... [-N] [-U]
                 [-E VAR [-A TOKEN] [-P TOKEN] [-I dir,-|+TOKEN]] [-C old=new]
                 [--] command ...
       $prog [VAR=TOKEN,TOKEN,...] [-E VAR] -L|-S
Flags:
   -help		Print this message and exit
   -A TOKEN		Append TOKEN to the path variable named 'VAR'
   -C olddir=newdir	Change <olddir> to <newdir> within 'VAR'
   -P TOKEN		Prepend TOKEN to the path variable named 'VAR'
   -I dir,(-|+)TOKEN]	Insert TOKEN before (-) or after (+) 'dir' in VAR
   -L [VAR]		List specified pathvar(s) in one-entry-per-line fmt
   -N			Remove entries which don't exist
   -R TOKEN		Remove specified dir from path
   -S [VAR]		Print specified pathvars in form suitable for `eval`
   -U			Remove redundant entries from path
   -W file		Like 'whence' ksh builtin - look for 'file' on PATH
Examples:
    $prog PATH=/tools/\@PLATFORM@/bin,\@PATH@ -- printenv PATH
    $prog CLASSPATH=\@CLASSPATH@,\@JAVA_HOME@/classes printenv CLASSPATH
    $prog -E LD_RUN_PATH -A /usr/openwin/lib -U -- ld ...
    $prog -E LD_RUN_PATH -I /usr/openwin/lib,-\@LD_LIBRARY_PATH@ ld ...
    $prog -L
    $prog -E CLASSPATH -L
    $prog -C /opt/netscape=/usr/local/netscape -L
    eval `$prog -N -U -R /usr/ucb -S`
    eval `$prog -E LD_RUN_PATH -I /usr/openwin/lib,-/usr/local/lib -S`
    $prog -W cat

In the above, TOKEN refers to a string which may optionally contain
references to environment variables in the form \@VAR@. These will be
replaced by the value \$VAR, and the commas will be replaced by the
appropriate path separator (':' or ';') for the current platform.
See "perldoc $prog" and "perldoc Env::Path" for full documentation.
EOF
    exit $rc;
}

sub expand {
    my $ev = shift;
    while (my($token) = ($ev =~ m%@(\w+)@%)) {
	$ev =~ s%\@$token@%$ENV{$token}%;
    }
    return $ev;
}

usage() if !@ARGV;

my @Paths;

while (my($var, $where, $str) = ($ARGV[0] =~ m%^(\w+)([=+]+)(.*)%)) {
    my $param = shift;
    push(@Paths, $var);
    my @val = split(/,/, $str);
    for (@val) { $_ = expand($_) }
    my $dsep = MSWIN ? ';' : ':';
    if ($where eq '=') {
	$ENV{$var} = join($dsep, @val);
    } elsif ($where eq '+=') {
	$ENV{$var} = join($dsep, @val, $ENV{$var});
    } elsif ($where eq '=+') {
	$ENV{$var} = join($dsep, $ENV{$var}, @val);
    } else {
	die "Error: $0: malformed parameter '$param'\n";
    }
}

my %opt;
my($opt_help, $opt_verbose);
{
    local $Getopt::Long::passthrough = 1;
    GetOptions('help' => \$opt_help, 'verbose' => \$opt_verbose);
    usage() if $opt_help;
}
local $Getopt::Long::order = $REQUIRE_ORDER;
GetOptions(\%opt, qw(Env=s
			    Append=s@ Change=s@ Prepend=s@ Insert=s@ Remove=s@
			    Nonexistent Uniqify
			    List:s@ Shell:s@ Whence=s)
);

usage() if !@ARGV && !($opt{List} || $opt{Shell} || $opt{Whence});

if (%opt) {
    require Env::Path;

    push(@Paths, $opt{Env}) if $opt{Env};
    push(@Paths, @{$opt{List}}) if $opt{List}->[0];
    push(@Paths, @{$opt{Shell}}) if $opt{Shell}->[0];
    push(@Paths, 'PATH') if !@Paths;

    my $var = $Paths[-1] || 'PATH';
    my $path = eval "Env::Path->$var";

    for (@{$opt{Prepend}}) { $path->Prepend(expand($_)) }

    for (@{$opt{Append}})  { $path->Append(expand($_)) }

    for (@{$opt{Remove}})  { $path->Remove(expand($_)) }

    for (@{$opt{Change}})  {
	my($old, $new) = split '=', $_, 2;
	$path->InsertBefore($old, $new);
	$path->Remove(expand($old))
    }

    $path->DeleteNonexistent if $opt{Nonexistent};

    $path->Uniqify if $opt{Uniqify};

    for (@{$opt{Insert}}) {
	if (!m%^(.+?),([+-])(.*)%) {
	    warn "Warning: $0: malformed -Insert parameter '$_'\n";
	    next;
	}
	my($marker, $where, $insert) = (expand($1), $2, expand($3));
	if ($where eq '-') {
	    $path->InsertBefore($marker, $insert);
	} else {
	    $path->InsertAfter($marker, $insert);
	}
    }

    if ($opt{List} && @{$opt{List}}) {
	usage(2) if ($opt{Shell} && @{$opt{Shell}}) || $opt{Whence};
	for my $pathvar (@Paths) {
	    my $path = eval "Env::Path->$pathvar";
	    for ($path->List) { print $_, "\n" }
	}
	exit 0;
    } elsif ($opt{Shell} && @{$opt{Shell}}) {
	usage(2) if $opt{Whence};
	for my $pathvar (@Paths) {
	    print Env::Path->$pathvar->Shell, "\n";
	}
	exit 0;
    } elsif ($opt{Whence}) {
	for my $pathvar (@Paths) {
	    my $path = eval "Env::Path->$pathvar";
	    for ($path->Whence($opt{Whence})) { print $_, "\n" }
	}
	exit 0;
    }
}

print STDERR "+ @ARGV\n" if $opt_verbose;
if (MSWIN) {
    exit system @ARGV;
} else {
    exec @ARGV;
    die "$0: $ARGV[0]: $!\n";
}

__END__

=head1 NAME

envpath - Advanced operations on path variables

=head1 SYNOPSIS

Run this script with the C<-help> option for usage details.

=head1 DESCRIPTION

Parses the command line, modifies the specified path variable(s), and
execs the remaining arguments. There are two modes, B<simple> and
B<advanced>:

=head2 SIMPLE MODE

Simple mode presents an alternative, platform-independent syntax for
specifying paths wherein the path separator is "," and environment
variables can be expanded with @NAME@. For example

    envpath PATH=@PATH@,/usr/ucb -- printenv PATH

appends C</usr/ucb> to C<$PATH> and execs I<printenv PATH>. The C<-->
is optional.

You can also specify prepending or appending by using C<+=> or C<=+>
respectively:

    # place /usr/ucb at the front
    envpath PATH+=/usr/ucb -- printenv PATH

    # place /usr/ucb at the back
    envpath PATH=+/usr/ucb -- printenv PATH

Simple mode requires only this script; it does not require Env::Path
to be installed.

=head2 ADVANCED MODE

Advanced mode basically provides command-line access to the features of
Env::Path (see), which must be installed. The C<-E> flag selects the
path variable to operate on and other flags specify operations on it.
E.g.

    envpath -E MANPATH -A /tmp -R /usr/share/man -N -U -- man ...

would take MANPATH, append /tmp to it, remove any references to
C</usr/share/man>, remove any dirs which don't exist (C<-N>) and
remove redundant entries (C<-U>) before running I<man>.

The -Whence option allows patterns. Thus

    envpath -W "cat*"

would find all programs on PATH which match cat*.

=head1 CLEARCASE WINKINS

A big part of the motivation for this script was for use with ClearCase
builds; iff you know or care about ClearCase read on. Typically, during
builds (and not just with ClearCase), pathvars such as PATH, CLASSPATH,
and LD_LIBRARY_PATH must be strictly controlled.  One choice is to
force static values of these into the environment during the build
process, another is to simply require/expect users to set their paths
appropriately. Each of these can lead to subtle build or runtime
errors, however, and makes it hard for new users to get up to speed
since their personal environment must be just so.

Another common choice is to use only full pathnames within the
Makefile, avoiding reliance on search paths at all. This is often the
best way to go but can suppress ClearCase winkins.  For example, say
you're generating ascii files of some type with a binary executable you
just built:

$(INCDIR)/foo.h: $(BINDIR)/foomaker
	$(BINDIR)/foomaker ...

The problem with this is that $(BINDIR) likely contains a platform part
such as 'solaris' or 'hpux', which makes it impossible to wink in the
foo.h file on other platforms even though it's ascii. This same thing
could come up even with a standard pre-built utility that's in
different places on different platforms; C<yacc>, for instance, is in
/usr/bin on Linux and /usr/ccs/bin on Solaris.

You could modify the path on the fly:

$(INCDIR)/foo.h: $(BINDIR)/foomaker
	PATH=$(BINDIR)$(SEP)$$PATH foomaker ...

but this suffers from the same problem: since $(BINDIR) and $PATH are
expanded literally within the build script they'll suppress winkins.
Here's a solution using I<envpath>:

$(INCDIR)/foo.h: $(BINDIR)/foomaker
	envpath PATH=@BINDIR@,@PATH@ foomaker ...

This hides the evaluation of BINDIR and PATH such that I<clearmake>
never sees anything but the literals, thus clearing the field for
winkins. Of course I<envpath> is capable of doing more than this, but
it's the original reason it was written.

=head1 AUTHOR

David Boyce <dsbperl AT boyski.com>

=head1 COPYRIGHT

Copyright (c) 2000-2001 David Boyce. All rights reserved.  This Perl
program is free software; you may redistribute and/or modify it under
the same terms as Perl itself.

=head1 SEE ALSO

perl(1), "perldoc Env::Path"

=cut
