path: root/lib/stdlib/doc/src/filename.xml

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<!DOCTYPE erlref SYSTEM "erlref.dtd">

<erlref>
  <header>
    <copyright>
      <year>1997</year><year>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
    </copyright>
    <legalnotice>
      Licensed under the Apache License, Version 2.0 (the "License");
      you may not use this file except in compliance with the License.
      You may obtain a copy of the License at
 
          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS,
      WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      See the License for the specific language governing permissions and
      limitations under the License.
    
    </legalnotice>

    <title>filename</title>
    <prepared>Kenneth Lundin</prepared>
    <docno>1</docno>
    <date>97-11-13</date>
    <rev>B</rev>
  </header>
  <module>filename</module>
  <modulesummary>Filename Manipulation Functions</modulesummary>
  <description>
    <p>The module <c>filename</c> provides a number of useful functions
      for analyzing and manipulating file names. These functions are
      designed so that the Erlang code can work on many different
      platforms with different formats for file names. With file name
      is meant all strings that can be used to denote a file. They can
      be short relative names like <c>foo.erl</c>, very long absolute
      name which include a drive designator and directory names like
      <c>D:\usr/local\bin\erl/lib\tools\foo.erl</c>, or any variations
      in between.</p>
    <p>In Windows, all functions return file names with forward slashes
      only, even if the arguments contain back slashes. Use
      <c>join/1</c> to normalize a file name by removing redundant
      directory separators.</p>
    <p>The module supports raw file names in the way that if a binary is present, or the file name cannot be interpreted according to the return value of 
    <seealso marker="kernel:file#native_name_encoding/0">file:native_name_encoding/0</seealso>, a raw file name will also be returned. For example filename:join/1 provided with a path component being a binary (and also not being possible to interpret under the current native file name encoding) will result in a raw file name being returned (the join operation will have been performed of course). For more information about raw file names, see the <seealso marker="kernel:file">file</seealso> module.</p>
  </description>
  <datatypes>
      <datatype>
          <name name="basedir_type"/>
      </datatype>
  </datatypes>
 
  <funcs>
    <func>
      <name name="absname" arity="1"/>
      <fsummary>Convert a filename to an absolute name, relative the working directory</fsummary>
      <desc>
        <p>Converts a relative <c><anno>Filename</anno></c> and returns an absolute
          name. No attempt is made to create the shortest absolute name,
          because this can give incorrect results on file systems which
          allow links.</p>
        <p>Unix examples:</p>
        <pre>
1> <input>pwd().</input>
"/usr/local"
2> <input>filename:absname("foo").</input>
"/usr/local/foo"
3> <input>filename:absname("../x").</input>
"/usr/local/../x"
4> <input>filename:absname("/").</input>
"/"</pre>
        <p>Windows examples:</p>
        <pre>
1> <input>pwd().</input>
"D:/usr/local"
2> <input>filename:absname("foo").</input>
"D:/usr/local/foo"
3> <input>filename:absname("../x").</input>
"D:/usr/local/../x"
4> <input>filename:absname("/").</input>
"D:/"</pre>
      </desc>
    </func>
    <func>
      <name name="absname" arity="2"/>
      <fsummary>Convert a filename to an absolute name, relative a specified directory</fsummary>
      <desc>
        <p>This function works like <c>absname/1</c>, except that
          the directory to which the file name should be made relative
          is given explicitly in the <c><anno>Dir</anno></c> argument.</p>
      </desc>
    </func>
    <func>
      <name name="absname_join" arity="2"/>
      <fsummary>Join an absolute directory with a relative filename</fsummary>
      <desc>
        <p>Joins an absolute directory with a relative filename.
          Similar to <c>join/2</c>, but on platforms with tight
          restrictions on raw filename length and no support for
          symbolic links (read: VxWorks), leading parent directory
          components in <c><anno>Filename</anno></c> are matched against trailing
          directory components in <c><anno>Dir</anno></c> so they can be removed
          from the result - minimizing its length.</p>
      </desc>
    </func>
    <func>
      <name name="basedir" arity="2"/>
      <fsummary>Equivalent to <c>basedir(<anno>Type</anno>,<anno>Application</anno>,#{})</c>.</fsummary>
      <desc>
          <p>
              Equivalent to <seealso marker="#basedir-3">
                  basedir(<anno>Type</anno>, <anno>Application</anno>, #{})</seealso>.
          </p>
      </desc>
    </func>
    <func>
      <name name="basedir" arity="3"/>
      <fsummary></fsummary>
      <desc><marker id="basedir-3"/>
          <p>
              Returns a suitable path, or paths, for a given type.
              If <c>os</c> is not set in <c><anno>Opts</anno></c> the function will default to
              the native option, i.e. <c>'linux'</c>, <c>'darwin'</c> or <c>'windows'</c>, as understood
              by <c>os:type/0</c>. Anything not recognized as <c>'darwin'</c> or <c>'windows'</c> is
              interpreted as <c>'linux'</c>.</p>
          <p>
              The options <c>'author'</c> and <c>'version'</c> are only used with <c>'windows'</c> option mode.
          </p>
        <list type="bulleted">
            <item><c>user_cache</c>
                <p>The path location is intended for transient data files on a local machine.</p>
                <p>
                    On Linux:
                    Respects the os environment variable <c>XDG_CACHE_HOME</c>.
                </p>
                <pre>
1> <input>filename:basedir(user_cache, "my_application", #{os=>linux}).</input>
"/home/otptest/.cache/my_application"</pre>
                On Darwin: <pre>
1> <input>filename:basedir(user_cache, "my_application", #{os=>darwin}).</input>
"/home/otptest/Library/Caches/my_application"</pre>
                On Windows: <pre>
1> <input>filename:basedir(user_cache, "My App").</input>
"c:/Users/otptest/AppData/Local/My App/Cache"
2> <input>filename:basedir(user_cache, "My App").</input>
"c:/Users/otptest/AppData/Local/My App/Cache"
3> <input>filename:basedir(user_cache, "My App", #{author=>"Erlang"}).</input>
"c:/Users/otptest/AppData/Local/Erlang/My App/Cache"
4> <input>filename:basedir(user_cache, "My App", #{version=>"1.2"}).</input>
"c:/Users/otptest/AppData/Local/My App/1.2/Cache"
5> <input>filename:basedir(user_cache, "My App", #{author=>"Erlang",version=>"1.2"}).</input>
"c:/Users/otptest/AppData/Local/Erlang/My App/1.2/Cache"</pre>
            </item>
            <item><c>user_config</c>
                <p>
                    The path location is intended for persistent configuration files.
                </p>
                <p>
                    On Linux:
                    Respects the os environment variable <c>XDG_CONFIG_HOME</c>.
                </p>
                <pre>
2> <input>filename:basedir(user_config, "my_application", #{os=>linux}).</input>
"/home/otptest/.config/my_application"</pre>
                On Darwin:<pre>
2> <input>filename:basedir(user_config, "my_application", #{os=>darwin}).</input>
"/home/otptest/Library/Application Support/my_application"</pre>
                On Windows:<pre>
1> <input>filename:basedir(user_config, "My App").</input>
"c:/Users/otptest/AppData/Roaming/My App"
2> <input>filename:basedir(user_config, "My App", #{author=>"Erlang", version=>"1.2"}).</input>
"c:/Users/otptest/AppData/Roaming/Erlang/My App/1.2"</pre>
            </item>
            <item><c>user_data</c>
                <p>
                    The path location is intended for persistent data files.
                </p>
                <p>
                    On Linux:
                    Respects the os environment variable <c>XDG_DATA_HOME</c>.
                </p>
                <pre>
3> <input>filename:basedir(user_data, "my_application", #{os=>linux}).</input>
"/home/otptest/.local/my_application"</pre>
                On Darwin:<pre>
3> <input>filename:basedir(user_data, "my_application", #{os=>darwin}).</input>
"/home/otptest/Library/Application Support/my_application"</pre>
                On Windows:<pre>
8> <input>filename:basedir(user_data, "My App").</input>
"c:/Users/otptest/AppData/Local/My App"
9> <input>filename:basedir(user_data, "My App",#{author=>"Erlang",version=>"1.2"}).</input>
"c:/Users/otptest/AppData/Local/Erlang/My App/1.2"</pre>
            </item>
            <item><c>user_log</c>
                <p>The path location is intended for transient log files on a local machine.</p>
                <p>
                On Linux:
                Respects the os environment variable <c>XDG_CACHE_HOME</c>.</p>
                <pre>
4> <input>filename:basedir(user_log, "my_application", #{os=>linux}).</input>
"/home/otptest/.cache/my_application/log"</pre>
                On Darwin:<pre>
4> <input>filename:basedir(user_log, "my_application", #{os=>darwin}).</input>
"/home/otptest/Library/Caches/my_application"</pre>
                On Windows:<pre>
12> <input>filename:basedir(user_log, "My App").</input>
"c:/Users/otptest/AppData/Local/My App/Logs"
13> <input>filename:basedir(user_log, "My App",#{author=>"Erlang",version=>"1.2"}).</input>
"c:/Users/otptest/AppData/Local/Erlang/My App/1.2/Logs"</pre>
            </item>
            <item><c>site_config</c><p>
                On Linux:
                Respects the os environment variable <c>XDG_CONFIG_DIRS</c>.</p>
<pre>
5> <input>filename:basedir(site_data, "my_application", #{os=>linux}).</input>
["/usr/local/share/my_application",
 "/usr/share/my_application"]
6> <input>os:getenv("XDG_CONFIG_DIRS").</input>
"/etc/xdg/xdg-ubuntu:/usr/share/upstart/xdg:/etc/xdg"
7> <input>filename:basedir(site_config, "my_application", #{os=>linux}).</input>
["/etc/xdg/xdg-ubuntu/my_application",
 "/usr/share/upstart/xdg/my_application",
 "/etc/xdg/my_application"]
8> <input>os:unsetenv("XDG_CONFIG_DIRS").</input>
true
9> <input>filename:basedir(site_config, "my_application", #{os=>linux}).</input>
["/etc/xdg/my_application"]</pre>
                On Darwin:<pre>
5> <input>filename:basedir(site_config, "my_application", #{os=>darwin}).</input>
["/Library/Application Support/my_application"]</pre>
            </item>
            <item><c>site_data</c><p>
                    On Linux:
                    Respects the os environment variable <c>XDG_DATA_DIRS</c>.</p>
                <pre>
10> <input>os:getenv("XDG_DATA_DIRS").</input>
"/usr/share/ubuntu:/usr/share/gnome:/usr/local/share/:/usr/share/"
11> <input>filename:basedir(site_data, "my_application", #{os=>linux}).</input>
["/usr/share/ubuntu/my_application",
 "/usr/share/gnome/my_application",
 "/usr/local/share/my_application",
 "/usr/share/my_application"]
12> <input>os:unsetenv("XDG_DATA_DIRS").</input>
true
13> <input>filename:basedir(site_data, "my_application", #{os=>linux}).</input>
["/usr/local/share/my_application",
 "/usr/share/my_application"]</pre>
                On Darwin:<pre>
5> <input>filename:basedir(site_data, "my_application", #{os=>darwin}).</input>
["/Library/Application Support/my_application"]</pre>
            </item>
        </list>
      </desc>
    </func>
    <func>
      <name name="basename" arity="1"/>
      <fsummary>Return the last component of a filename</fsummary>
      <desc>
        <p>Returns the last component of <c><anno>Filename</anno></c>, or
          <c><anno>Filename</anno></c> itself if it does not contain any directory
          separators.</p>
        <pre>
5> <input>filename:basename("foo").</input>
"foo"
6> <input>filename:basename("/usr/foo").</input>
"foo"
7> <input>filename:basename("/").</input>
[]</pre>
      </desc>
    </func>
    <func>
      <name name="basename" arity="2"/>
      <fsummary>Return the last component of a filename, stripped of the specified extension</fsummary>
      <desc>
        <p>Returns the last component of <c><anno>Filename</anno></c> with the
          extension <c><anno>Ext</anno></c> stripped. This function should be used
          to remove a specific extension which might, or might not, be
          there. Use <c>rootname(basename(Filename))</c> to remove an
          extension that exists, but you are not sure which one it is.</p>
        <pre>
8> <input>filename:basename("~/src/kalle.erl", ".erl").</input>
"kalle"
9> <input>filename:basename("~/src/kalle.beam", ".erl").</input>
"kalle.beam"
10> <input>filename:basename("~/src/kalle.old.erl", ".erl").</input>
"kalle.old"
11> <input>filename:rootname(filename:basename("~/src/kalle.erl")).</input>
"kalle"
12> <input>filename:rootname(filename:basename("~/src/kalle.beam")).</input>
"kalle"</pre>
      </desc>
    </func>
    <func>
      <name name="dirname" arity="1"/>
      <fsummary>Return the directory part of a path name</fsummary>
      <desc>
        <p>Returns the directory part of <c><anno>Filename</anno></c>.</p>
        <pre>
13> <input>filename:dirname("/usr/src/kalle.erl").</input>
"/usr/src"
14> <input>filename:dirname("kalle.erl").</input>
"."

5> <input>filename:dirname("\\usr\\src/kalle.erl").</input> % Windows
"/usr/src"</pre>
      </desc>
    </func>
    <func>
      <name name="extension" arity="1"/>
      <fsummary>Return the file extension</fsummary>
      <desc>
        <p>Returns the file extension of <c><anno>Filename</anno></c>, including
          the period. Returns an empty string if there is no extension.</p>
        <pre>
15> <input>filename:extension("foo.erl").</input>
".erl"
16> <input>filename:extension("beam.src/kalle").</input>
[]</pre>
      </desc>
    </func>
    <func>
      <name name="flatten" arity="1"/>
      <fsummary>Convert a filename to a flat string</fsummary>
      <desc>
        <p>Converts a possibly deep list filename consisting of
          characters and atoms into the corresponding flat string
          filename.</p>
      </desc>
    </func>
    <func>
      <name name="join" arity="1"/>
      <fsummary>Join a list of filename components with directory separators</fsummary>
      <desc>
        <p>Joins a list of file name <c><anno>Components</anno></c> with directory
          separators. If one of the elements of <c><anno>Components</anno></c>
          includes an absolute path, for example <c>"/xxx"</c>,
          the preceding elements, if any, are removed from the result.</p>
        <p>The result is "normalized":</p>
        <list type="bulleted">
          <item>Redundant directory separators are removed.</item>
          <item>In Windows, all directory separators are forward
           slashes and the drive letter is in lower case.</item>
        </list>
        <pre>
17> <input>filename:join(["/usr", "local", "bin"]).</input>
"/usr/local/bin"
18> <input>filename:join(["a/b///c/"]).</input>
"a/b/c"

6> <input>filename:join(["B:a\\b///c/"]).</input> % Windows
"b:a/b/c"</pre>
      </desc>
    </func>
    <func>
      <name name="join" arity="2"/>
      <fsummary>Join two filename components with directory separators</fsummary>
      <desc>
        <p>Joins two file name components with directory separators. 
          Equivalent to <c>join([<anno>Name1</anno>, <anno>Name2</anno>])</c>.</p>
      </desc>
    </func>
    <func>
      <name name="nativename" arity="1"/>
      <fsummary>Return the native form of a file path</fsummary>
      <desc>
        <p>Converts <c><anno>Path</anno></c> 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 <c>join/1</c>.</p>
        <pre>
19> <input>filename:nativename("/usr/local/bin/").</input> % Unix
"/usr/local/bin"

7> <input>filename:nativename("/usr/local/bin/").</input> % Windows
"\\usr\\local\\bin"</pre>
      </desc>
    </func>
    <func>
      <name name="pathtype" arity="1"/>
      <fsummary>Return the type of a path</fsummary>
      <desc>
        <p>Returns the type of path, one of <c>absolute</c>,
          <c>relative</c>, or <c>volumerelative</c>.</p>
        <taglist>
          <tag><c>absolute</c></tag>
          <item>
            <p>The path name refers to a specific file on a specific
              volume.</p>
            <p>Unix example: <c>/usr/local/bin</c></p>
            <p>Windows example: <c>D:/usr/local/bin</c></p>
          </item>
          <tag><c>relative</c></tag>
          <item>
            <p>The path name is relative to the current working
              directory on the current volume.</p>
            <p>Example: <c>foo/bar, ../src</c></p>
          </item>
          <tag><c>volumerelative</c></tag>
          <item>
            <p>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.</p>
            <p>Windows example: <c>D:bar.erl, /bar/foo.erl</c></p>
          </item>
        </taglist>
      </desc>
    </func>
    <func>
      <name name="rootname" arity="1"/>
      <name name="rootname" arity="2"/>
      <fsummary>Remove a filename extension</fsummary>
      <desc>
        <p>Remove a filename extension. <c>rootname/2</c> works as
          <c>rootname/1</c>, except that the extension is removed only
          if it is <c><anno>Ext</anno></c>.</p>
        <pre>
20> <input>filename:rootname("/beam.src/kalle").</input>
/beam.src/kalle"
21> <input>filename:rootname("/beam.src/foo.erl").</input>
"/beam.src/foo"
22> <input>filename:rootname("/beam.src/foo.erl", ".erl").</input>
"/beam.src/foo"
23> <input>filename:rootname("/beam.src/foo.beam", ".erl").</input>
"/beam.src/foo.beam"</pre>
      </desc>
    </func>
    <func>
      <name name="split" arity="1"/>
      <fsummary>Split a filename into its path components</fsummary>
      <desc>
        <p>Returns a list whose elements are the path components of
          <c><anno>Filename</anno></c>.</p>
        <pre>
24> <input>filename:split("/usr/local/bin").</input>
["/","usr","local","bin"]
25> <input>filename:split("foo/bar").</input>
["foo","bar"]
26> <input>filename:split("a:\\msdev\\include").</input>
["a:/","msdev","include"]</pre>
      </desc>
    </func>
    <func>
      <name name="find_src" arity="1"/>
      <name name="find_src" arity="2"/>
      <fsummary>Find the filename and compiler options for a module</fsummary>
      <desc>
        <p>Finds the source filename and compiler options for a module.
          The result can be fed to <c>compile:file/2</c> in order to
          compile the file again.</p>

	<warning><p>We don't recommend using this function. If possible,
	use <seealso marker="beam_lib">beam_lib(3)</seealso> to extract
	the abstract code format from the BEAM file and compile that
	instead.</p></warning>

        <p>The <c><anno>Beam</anno></c> argument, which can be a string or an atom,
          specifies either the module name or the path to the source
          code, with or without the <c>".erl"</c> extension. In either
          case, the module must be known by the code server, i.e.
          <c>code:which(<anno>Module</anno>)</c> must succeed.</p>
        <p><c><anno>Rules</anno></c> describes how the source directory can be found,
          when the object code directory is known. It is a list of
          tuples <c>{<anno>BinSuffix</anno>, <anno>SourceSuffix</anno>}</c> and is interpreted
          as follows: If the end of the directory name where the object
          is located matches <c><anno>BinSuffix</anno></c>, then the source code
          directory has the same name, but with <c><anno>BinSuffix</anno></c>
          replaced by <c><anno>SourceSuffix</anno></c>. <c><anno>Rules</anno></c> defaults to:</p>
        <code type="none">
[{"", ""}, {"ebin", "src"}, {"ebin", "esrc"}]</code>
        <p>If the source file is found in the resulting directory, then
          the function returns that location together with
          <c><anno>Options</anno></c>. Otherwise, the next rule is tried, and so on.</p>

        <p>The function returns <c>{<anno>SourceFile</anno>, <anno>Options</anno>}</c> if it succeeds.
          <c><anno>SourceFile</anno></c> is the absolute path to the source file
          without the <c>".erl"</c> extension. <c><anno>Options</anno></c> include
          the options which are necessary to recompile the file with
          <c>compile:file/2</c>, but excludes options such as
          <c>report</c> or <c>verbose</c> which do not change the way
          code is generated. The paths in the <c>{outdir, <anno>Path</anno>}</c>
          and <c>{i, Path}</c> options are guaranteed to be
          absolute.</p>

      </desc>
    </func>
  </funcs>
</erlref>