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# filename (stdlib v6.2.2.2)

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Filename manipulation functions.

This module provides functions for analyzing and manipulating filenames. These functions are designed so that the Erlang code can work on many different platforms with different filename formats. With filename is meant all strings that can be used to denote a file. The filename can be a short relative name like `foo.erl`, a long absolute name including a drive designator, a directory name like `D:\usr/local\bin\erl/lib\tools\foo.erl`, or any variations in between.

In Windows, all functions return filenames with forward slashes only, even if the arguments contain backslashes. To normalize a filename by removing redundant directory separators, use `join/1`.

The module supports raw filenames in the way that if a binary is present, or the filename cannot be interpreted according to the return value of `file:native_name_encoding/0`, a raw filename is also returned. For example, `join/1` provided with a path component that is a binary (and cannot be interpreted under the current native filename encoding) results in a raw filename that is returned (the join operation is performed of course). For more information about raw filenames, see the `file` module.

#### Note

Functionality in this module generally assumes valid input and does not necessarily fail on input that does not use a valid encoding, but may instead very likely produce invalid output.

File operations used to accept filenames containing null characters (integer value zero). This caused the name to be truncated and in some cases arguments to primitive operations to be mixed up. Filenames containing null characters inside the filename are now rejected and will cause primitive file operations to fail.

#### Warning

Currently null characters at the end of the filename will be accepted by primitive file operations. Such filenames are however still documented as invalid. The implementation will also change in the future and reject such filenames.

# Summary

## Types

basedir_opts()
basedir_path_type()
basedir_paths_type()

## Functions

absname(Filename)

Converts a relative `Filename` and returns an absolute name. No attempt is made to create the shortest absolute name, as this can give incorrect results on file systems that allow links.

absname(Filename, Dir)

Same as `absname/1`, except that the directory to which the filename is to be made relative is specified in argument `Dir`.

absname_join(Dir, Filename)

Joins an absolute directory with a relative filename.

basedir(Type, Application)

Equivalent to basedir(PathType, Application, #{}) or basedir(PathsType, Application, #{}).

basedir(Type, Application, Opts)

basename(Filename)

Returns the last component of `Filename`, or `Filename` itself if it does not contain any directory separators.

basename(Filename, Ext)

Returns the last component of `Filename` with extension `Ext` stripped.

dirname(Filename)

Returns the directory part of `Filename`.

extension(Filename)

Returns the file extension of `Filename`, including the period. Returns an empty string if no extension exists.

flatten(Filename)

Converts a possibly deep list filename consisting of characters and atoms into the corresponding flat string filename.

join(Components)

Joins a list of filename `Components` with directory separators. If one of the elements of `Components` includes an absolute path, such as `"/xxx"`, the preceding elements, if any, are removed from the result.

join(Name1, Name2)

Joins two filename components with directory separators. Equivalent to `join([Name1, Name2])`.

nativename(Path)

Converts `Path` to a form accepted by the command shell and native applications on the current platform. On Windows, forward slashes are converted to backward slashes. On all platforms, the name is normalized as done by `join/1`.

pathtype(Path)

Returns the path type, which is one of the following

rootname(Filename)

Removes the filename extension.

rootname(Filename, Ext)

Removes the filename extension `Ext` from `Filename`.

split(Filename)

Returns a list whose elements are the path components of `Filename`.

# Types

# basedir_opts()

(not exported)

    -type basedir_opts() ::
              #{author => string() | binary(),
                os => windows | darwin | linux,
                version => string() | binary()}.

# basedir_path_type()

(not exported)

    -type basedir_path_type() :: user_cache | user_config | user_data | user_log.

# basedir_paths_type()

(not exported)

    -type basedir_paths_type() :: site_config | site_data.

# Functions

# absname(Filename)

    -spec absname(Filename) -> file:filename_all() when Filename :: file:name_all().

Converts a relative `Filename` and returns an absolute name. No attempt is made to create the shortest absolute name, as this can give incorrect results on file systems that allow links.

Unix examples:

    1> pwd().
    "/usr/local"
    2> filename:absname("foo").
    "/usr/local/foo"
    3> filename:absname("../x").
    "/usr/local/../x"
    4> filename:absname("/").
    "/"

Windows examples:

    1> pwd().
    "D:/usr/local"
    2> filename:absname("foo").
    "D:/usr/local/foo"
    3> filename:absname("../x").
    "D:/usr/local/../x"
    4> filename:absname("/").
    "D:/"

# absname(Filename, Dir)

    -spec absname(Filename, Dir) -> file:filename_all()
                     when Filename :: file:name_all(), Dir :: file:name_all().

Same as `absname/1`, except that the directory to which the filename is to be made relative is specified in argument `Dir`.

# absname_join(Dir, Filename)

    -spec absname_join(Dir, Filename) -> file:filename_all()
                          when Dir :: file:name_all(), Filename :: file:name_all().

Joins an absolute directory with a relative filename.

Similar to `join/2`, but on platforms with tight restrictions on raw filename length and no support for symbolic links, leading parent directory components in `Filename` are matched against trailing directory components in `Dir` so they can be removed from the result - minimizing its length.

# basedir(Type, Application)

(since OTP 19.0)

    -spec basedir(PathType, Application) -> file:filename_all()
                     when PathType :: basedir_path_type(), Application :: string() | binary();
                 (PathsType, Application) -> [file:filename_all()]
                     when PathsType :: basedir_paths_type(), Application :: string() | binary().

Equivalent to basedir(PathType, Application, #{}) or basedir(PathsType, Application, #{}).

# basedir(Type, Application, Opts)

(since OTP 19.0)

    -spec basedir(PathType, Application, Opts) -> file:filename_all()
                     when
                         PathType :: basedir_path_type(),
                         Application :: string() | binary(),
                         Opts :: basedir_opts();
                 (PathsType, Application, Opts) -> [file:filename_all()]
                     when
                         PathsType :: basedir_paths_type(),
                         Application :: string() | binary(),
                         Opts :: basedir_opts().

Returns a suitable path, or paths, for a given type. If `os` is not set in `Opts` the function will default to the native option, that is `'linux'`, `'darwin'` or `'windows'`, as understood by `os:type/0`. Anything not recognized as `'darwin'` or `'windows'` is interpreted as `'linux'`.

The options `'author'` and `'version'` are only used with `'windows'` option mode.

- `user_cache`

  The path location is intended for transient data files on a local machine.

  On Linux: Respects the os environment variable `XDG_CACHE_HOME`.

      1> filename:basedir(user_cache, "my_application", #{os=>linux}).
      "/home/otptest/.cache/my_application"

  On Darwin:

      1> filename:basedir(user_cache, "my_application", #{os=>darwin}).
      "/home/otptest/Library/Caches/my_application"

  On Windows:

      1> filename:basedir(user_cache, "My App").
      "c:/Users/otptest/AppData/Local/My App/Cache"
      2> filename:basedir(user_cache, "My App").
      "c:/Users/otptest/AppData/Local/My App/Cache"
      3> filename:basedir(user_cache, "My App", #{author=>"Erlang"}).
      "c:/Users/otptest/AppData/Local/Erlang/My App/Cache"
      4> filename:basedir(user_cache, "My App", #{version=>"1.2"}).
      "c:/Users/otptest/AppData/Local/My App/1.2/Cache"
      5> filename:basedir(user_cache, "My App", #{author=>"Erlang",version=>"1.2"}).
      "c:/Users/otptest/AppData/Local/Erlang/My App/1.2/Cache"

- `user_config`

  The path location is intended for persistent configuration files.

  On Linux: Respects the os environment variable `XDG_CONFIG_HOME`.

      2> filename:basedir(user_config, "my_application", #{os=>linux}).
      "/home/otptest/.config/my_application"

  On Darwin:

      2> filename:basedir(user_config, "my_application", #{os=>darwin}).
      "/home/otptest/Library/Application Support/my_application"

  On Windows:

      1> filename:basedir(user_config, "My App").
      "c:/Users/otptest/AppData/Roaming/My App"
      2> filename:basedir(user_config, "My App", #{author=>"Erlang", version=>"1.2"}).
      "c:/Users/otptest/AppData/Roaming/Erlang/My App/1.2"

- `user_data`

  The path location is intended for persistent data files.

  On Linux: Respects the os environment variable `XDG_DATA_HOME`.

      3> filename:basedir(user_data, "my_application", #{os=>linux}).
      "/home/otptest/.local/my_application"

  On Darwin:

      3> filename:basedir(user_data, "my_application", #{os=>darwin}).
      "/home/otptest/Library/Application Support/my_application"

  On Windows:

      8> filename:basedir(user_data, "My App").
      "c:/Users/otptest/AppData/Local/My App"
      9> filename:basedir(user_data, "My App",#{author=>"Erlang",version=>"1.2"}).
      "c:/Users/otptest/AppData/Local/Erlang/My App/1.2"

- `user_log`

  The path location is intended for transient log files on a local machine.

  On Linux: Respects the os environment variable `XDG_CACHE_HOME`.

      4> filename:basedir(user_log, "my_application", #{os=>linux}).
      "/home/otptest/.cache/my_application/log"

  On Darwin:

      4> filename:basedir(user_log, "my_application", #{os=>darwin}).
      "/home/otptest/Library/Logs/my_application"

  On Windows:

      12> filename:basedir(user_log, "My App").
      "c:/Users/otptest/AppData/Local/My App/Logs"
      13> filename:basedir(user_log, "My App",#{author=>"Erlang",version=>"1.2"}).
      "c:/Users/otptest/AppData/Local/Erlang/My App/1.2/Logs"

- `site_config`

  On Linux: Respects the os environment variable `XDG_CONFIG_DIRS`.

      5> filename:basedir(site_config, "my_application", #{os=>linux}).
      ["/usr/local/share/my_application",
       "/usr/share/my_application"]
      6> os:getenv("XDG_CONFIG_DIRS").
      "/etc/xdg/xdg-ubuntu:/usr/share/upstart/xdg:/etc/xdg"
      7> filename:basedir(site_config, "my_application", #{os=>linux}).
      ["/etc/xdg/xdg-ubuntu/my_application",
       "/usr/share/upstart/xdg/my_application",
       "/etc/xdg/my_application"]
      8> os:unsetenv("XDG_CONFIG_DIRS").
      true
      9> filename:basedir(site_config, "my_application", #{os=>linux}).
      ["/etc/xdg/my_application"]

  On Darwin:

      5> filename:basedir(site_config, "my_application", #{os=>darwin}).
      ["/Library/Application Support/my_application"]

- `site_data`

  On Linux: Respects the os environment variable `XDG_DATA_DIRS`.

      10> os:getenv("XDG_DATA_DIRS").
      "/usr/share/ubuntu:/usr/share/gnome:/usr/local/share/:/usr/share/"
      11> filename:basedir(site_data, "my_application", #{os=>linux}).
      ["/usr/share/ubuntu/my_application",
       "/usr/share/gnome/my_application",
       "/usr/local/share/my_application",
       "/usr/share/my_application"]
      12> os:unsetenv("XDG_DATA_DIRS").
      true
      13> filename:basedir(site_data, "my_application", #{os=>linux}).
      ["/usr/local/share/my_application",
       "/usr/share/my_application"]

  On Darwin:

      5> filename:basedir(site_data, "my_application", #{os=>darwin}).
      ["/Library/Application Support/my_application"]

# basename(Filename)

    -spec basename(Filename) -> file:filename_all() when Filename :: file:name_all().

Returns the last component of `Filename`, or `Filename` itself if it does not contain any directory separators.

Examples:

    5> filename:basename("foo").
    "foo"
    6> filename:basename("/usr/foo").
    "foo"
    7> filename:basename("/").
    []

# basename(Filename, Ext)

    -spec basename(Filename, Ext) -> file:filename_all()
                      when Filename :: file:name_all(), Ext :: file:name_all().

Returns the last component of `Filename` with extension `Ext` stripped.

This function is to be used to remove a (possible) specific extension. To remove an existing extension when you are unsure which one it is, use `rootname(basename(Filename))`.

Examples:

    8> filename:basename("~/src/kalle.erl", ".erl").
    "kalle"
    9> filename:basename("~/src/kalle.beam", ".erl").
    "kalle.beam"
    10> filename:basename("~/src/kalle.old.erl", ".erl").
    "kalle.old"
    11> filename:rootname(filename:basename("~/src/kalle.erl")).
    "kalle"
    12> filename:rootname(filename:basename("~/src/kalle.beam")).
    "kalle"

# dirname(Filename)

    -spec dirname(Filename) -> file:filename_all() when Filename :: file:name_all().

Returns the directory part of `Filename`.

Examples:

    13> filename:dirname("/usr/src/kalle.erl").
    "/usr/src"
    14> filename:dirname("kalle.erl").
    "."

    5> filename:dirname("\\usr\\src/kalle.erl"). % Windows
    "/usr/src"

# extension(Filename)

    -spec extension(Filename) -> file:filename_all() when Filename :: file:name_all().

Returns the file extension of `Filename`, including the period. Returns an empty string if no extension exists.

Examples:

    15> filename:extension("foo.erl").
    ".erl"
    16> filename:extension("beam.src/kalle").
    []

# flatten(Filename)

    -spec flatten(Filename) -> file:filename_all() when Filename :: file:name_all().

Converts a possibly deep list filename consisting of characters and atoms into the corresponding flat string filename.

# join(Components)

    -spec join(Components) -> file:filename_all() when Components :: [file:name_all()].

Joins a list of filename `Components` with directory separators. If one of the elements of `Components` includes an absolute path, such as `"/xxx"`, the preceding elements, if any, are removed from the result.

The result is "normalized":

- Redundant directory separators are removed.
- In Windows, all directory separators are forward slashes and the drive letter is in lower case.

Examples:

    17> filename:join(["/usr", "local", "bin"]).
    "/usr/local/bin"
    18> filename:join(["a/b///c/"]).
    "a/b/c"

    6> filename:join(["B:a\\b///c/"]). % Windows
    "b:a/b/c"

# join(Name1, Name2)

    -spec join(Name1, Name2) -> file:filename_all() when Name1 :: file:name_all(), Name2 :: file:name_all().

Joins two filename components with directory separators. Equivalent to `join([Name1, Name2])`.

# nativename(Path)

    -spec nativename(Path) -> file:filename_all() when Path :: file:name_all().

Converts `Path` to a form accepted by the command shell and native applications on the current platform. On Windows, forward slashes are converted to backward slashes. On all platforms, the name is normalized as done by `join/1`.

Examples:

    19> filename:nativename("/usr/local/bin/"). % Unix
    "/usr/local/bin"

    7> filename:nativename("/usr/local/bin/"). % Windows
    "\\usr\\local\\bin"

# pathtype(Path)

    -spec pathtype(Path) -> absolute | relative | volumerelative when Path :: file:name_all().

Returns the path type, which is one of the following:

- `absolute` - The path name refers to a specific file on a specific volume.

  Unix example: `/usr/local/bin`

  Windows example: `D:/usr/local/bin`

- `relative` - The path name is relative to the current working directory on the current volume.

  Example: `foo/bar, ../src`

- `volumerelative` - The path name is relative to the current working directory on a specified volume, or it is a specific file on the current working volume.

  Windows example: `D:bar.erl, /bar/foo.erl`

# rootname(Filename)

    -spec rootname(Filename) -> file:filename_all() when Filename :: file:name_all().

Removes the filename extension.

Examples:

    1> filename:rootname("/beam.src/kalle").
    "/beam.src/kalle"
    2> filename:rootname("/beam.src/foo.erl").
    "/beam.src/foo"

# rootname(Filename, Ext)

    -spec rootname(Filename, Ext) -> file:filename_all()
                      when Filename :: file:name_all(), Ext :: file:name_all().

Removes the filename extension `Ext` from `Filename`.

Examples:

    1> filename:rootname("/beam.src/foo.erl", ".erl").
    "/beam.src/foo"
    2> filename:rootname("/beam.src/foo.beam", ".erl").
    "/beam.src/foo.beam"

# split(Filename)

    -spec split(Filename) -> Components when Filename :: file:name_all(), Components :: [file:name_all()].

Returns a list whose elements are the path components of `Filename`.

Examples:

    24> filename:split("/usr/local/bin").
    ["/","usr","local","bin"]
    25> filename:split("foo/bar").
    ["foo","bar"]
    26> filename:split("a:\\msdev\\include").
    ["a:/","msdev","include"]