path: root/erts/doc/src/escript.xml

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<!DOCTYPE comref SYSTEM "comref.dtd">

<comref>
  <header>
    <copyright>
      <year>2007</year><year>2017</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
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    </legalnotice>

    <title>escript</title>
    <prepared></prepared>
    <docno></docno>
    <date></date>
    <rev></rev>
    <file>escript.xml</file>
  </header>
  <com>escript</com>
  <comsummary>Erlang scripting support</comsummary>
  <description>
    <p><c>escript</c> provides support for running short Erlang programs
      without having to compile them first, and an easy way to retrieve the
      command-line arguments.</p>

      <p>It is possible to bundle <c>escript</c>(s) with an Erlang
      runtime system to make it self-sufficient and relocatable. In such
      a standalone system, the <c>escript</c>(s) should be located in
      the top <c>bin</c> directory of the standalone system and given
      <c>.escript</c> as file extension. Further the (built-in)
      <c>escript</c> program should be copied to the same directory and
      given the scripts original name (without the <c>.escript</c>
      extension). This will enable use of the bundled Erlang runtime
      system.</p>

      <p>The (built-in) <c>escript</c> program first determines which
      Erlang runtime system to use and then starts it to execute your
      script. Usually the runtime system is located in the same Erlang
      installation as the <c>escript</c> program itself. But for
      standalone systems with one or more escripts it may be the case
      that the <c>escript</c> program in your path actually starts the
      runtime system bundled with the escript. This is intentional, and
      typically happens when the standalone system <c>bin</c> directory is not
      in the execution path (as it may cause its <c>erl</c> program to
      override the desired one) and the <c>escript</c>(s) are referred to via
      symbolic links from a <c>bin</c> directory in the path.</p>
  </description>

  <funcs>
    <func>
      <name>script-name script-arg1 script-arg2...</name>
      <name>escript escript-flags script-name script-arg1 script-arg2...</name>
      <fsummary>Run a script written in Erlang.</fsummary>
      <desc>
        <p><c>escript</c> runs a script written in Erlang.</p>
        <p>Example:</p>
        <pre>
$ <input>chmod u+x factorial</input>
$ <input>cat factorial</input>
#!/usr/bin/env escript
%% -*- erlang -*-
%%! -smp enable -sname factorial -mnesia debug verbose
main([String]) ->
    try
        N = list_to_integer(String),
        F = fac(N),
        io:format("factorial ~w = ~w\n", [N,F])
    catch
        _:_ ->
            usage()
    end;
main(_) ->
    usage().

usage() ->
    io:format("usage: factorial integer\n"),
    halt(1).

fac(0) -> 1;
fac(N) -> N * fac(N-1).
$ <input>./factorial 5</input>
factorial 5 = 120
$ <input>./factorial</input>
usage: factorial integer
$ <input>./factorial five</input>
usage: factorial integer</pre>
        <p>The header of the Erlang script in the example differs from
          a normal Erlang module. The first line is intended to be the
          interpreter line, which invokes <c>escript</c>.</p>
        <p>However, if you invoke the <c>escript</c> as follows,
          the contents of the first line does not matter, but it
          cannot contain Erlang code as it will be ignored:</p>
        <pre>
$ <input>escript factorial 5</input></pre>
        <p>The second line in the example contains an optional
          directive to the <c>Emacs</c> editor, which causes it to
          enter the major mode for editing Erlang source files. If the
          directive is present, it must be located on the second
          line.</p>
        <p>If a comment selecting the <seealso
          marker="stdlib:epp#encoding">encoding</seealso> exists, it can be
          located on the second line.</p>
        <note>
          <p>The encoding specified by the above mentioned comment
            applies to the script itself. The encoding of the
            I/O-server, however, must be set explicitly as follows:</p>
          <code>
io:setopts([{encoding, unicode}])</code>
          <p>The default encoding of the I/O-server for <c>standard_io</c>
            is <c>latin1</c>, as the script runs in a non-interactive terminal
            (see section
            <seealso marker="stdlib:unicode_usage#unicode_options_summary">
            Summary of Options</seealso>) in the STDLIB User's Guide.</p>
        </note>
        <p>On the third line (or second line depending on the presence
          of the Emacs directive), arguments can be specified to
          the emulator, for example:</p>
        <pre>
%%! -smp enable -sname factorial -mnesia debug verbose</pre>
        <p>Such an argument line must start with <c>%%!</c> and the
          remaining line is interpreted as arguments to the emulator.</p>
        <p>If you know the location of the <c>escript</c> executable, the first
          line can directly give the path to <c>escript</c>, for example:</p>
        <pre>
#!/usr/local/bin/escript</pre>
        <p>As any other type of scripts, Erlang scripts do not work on
          Unix platforms if the execution bit for the script file is not set.
          (To turn on the execution bit, use <c>chmod +x script-name</c>.)</p>
        <p>The remaining Erlang script file can either contain
          Erlang <em>source code</em>, an <em>inlined beam file</em>, or an
          <em>inlined archive file</em>.</p>
        <p>An Erlang script file must always contain the <c>main/1</c>
          function. When the script is run, the
          <c>main/1</c> function is called with a list
          of strings representing the arguments specified to the script (not
          changed or interpreted in any way).</p>
        <p>If the <c>main/1</c> function in the script returns successfully,
          the exit status for the script is <c>0</c>. If an exception is
          generated during execution, a short message is printed and the script
          terminates with exit status <c>127</c>.</p>
        <p>To return your own non-zero exit code, call <c>halt(ExitCode)</c>,
          for example:</p>
        <pre>
halt(1).</pre>
        <p>To retrieve the pathname of the script, call
          <seealso marker="#script_name_0">
          <c>escript:script_name()</c></seealso> from your script
	  (the pathname is usually, but not always, absolute).</p>
        <p>If the file contains source code (as in the example above),
          it is processed by the
          <seealso marker="stdlib:epp"><c>epp</c></seealso> preprocessor.
          This means that you, for example, can use predefined macros
          (such as <c>?MODULE</c>) and include directives like
          the <c>-include_lib</c> directive. For example, use</p>
        <pre>
-include_lib("kernel/include/file.hrl").</pre>
        <p>to include the record definitions for the records used by function
          <seealso marker="kernel:file#read_link_info/1">
          <c>file:read_link_info/1</c></seealso>. You can also select
          encoding by including an encoding comment here, but if
          a valid encoding comment exists on the second line, it takes
          precedence.</p>
        <p>The script is checked for syntactic and semantic
          correctness before it is run. If there are warnings (such as
          unused variables), they are printed and the script will
          still be run. If there are errors, they are printed and
          the script will not be run and its exit status is
          <c>127</c>.</p>
        <p>Both the module declaration and the export declaration of
          the <c>main/1</c> function are optional.</p>
        <p>By default, the script will be interpreted. You can force
          it to be compiled by including the following line somewhere
          in the script file:</p>
        <pre>
-mode(compile).</pre>
        <p>Execution of interpreted code is slower than compiled code.
          If much of the execution takes place in interpreted code, it
          can be worthwhile to compile it, although the compilation
          itself takes a little while. Also, <c>native</c> can be supplied
          instead of <c>compile</c>. This compiles the script
          using the native flag and may or may not be worthwhile
          depending on the escript characteristics.</p>
        <p>As mentioned earlier, a script can
          contains precompiled <c>beam</c> code. In a precompiled
          script, the interpretation of the script header is
          the same as in a script containing source code. This means
          that you can make a <c>beam</c> file executable by
          prepending the file with the lines starting with <c>#!</c>
          and <c>%%!</c> mentioned above. In a precompiled script, the
          <c>main/1</c> function must be exported.</p>
        <p>Another option is to have an entire
          Erlang archive in the script. In an archive script, the
          interpretation of the script header is the same as
          in a script containing source code. This means that you can
          make an archive file executable by prepending the file with
          the lines starting with <c>#!</c> and <c>%%!</c> mentioned
          above. In an archive script, the <c>main/1</c> function must
          be exported. By default the <c>main/1</c> function in the
          module with the same name as the basename of the
          <c>escript</c> file is invoked. This behavior can be
          overridden by setting flag <c>-escript main Module</c>
          as one of the emulator flags. <c>Module</c> must be the
          name of a module that has an exported <c>main/1</c>
          function. For more information about archives and code loading, see
          <seealso marker="kernel:code"><c>code(3)</c></seealso>.</p>
        <p>It is often very convenient to have a header in
          the escript, especially on Unix platforms. However, the header
          is optional, so you directly can "execute"
          an Erlang module, Beam file, or archive file without adding
          any header to them. But then you have to invoke the script
          as follows:</p>
        <pre>
$ <input>escript factorial.erl 5</input>
factorial 5 = 120
$ <input>escript factorial.beam 5</input>
factorial 5 = 120
$ <input>escript factorial.zip 5</input>
factorial 5 = 120</pre>
      </desc>
    </func>

    <func>
      <name>escript:create(FileOrBin, Sections) -> ok | {ok, binary()} |
        {error, term()}</name>
      <fsummary>Create an escript.</fsummary>
      <type>
        <v>FileOrBin = filename() | 'binary'</v>
        <v>Sections = [Header] Body | Body</v>
        <v>Header = shebang | {shebang, Shebang}
        &nbsp;&nbsp;&nbsp;| comment | {comment, Comment}
        &nbsp;&nbsp;&nbsp;| {emu_args, EmuArgs}</v>
        <v>Shebang = string() | 'default' | 'undefined'</v>
        <v>Comment = string() | 'default' | 'undefined'</v>
        <v>EmuArgs = string() | 'undefined'</v>
        <v>Body = {source, SourceCode} | {beam, BeamCode}
        &nbsp;&nbsp;&nbsp;| {archive, ZipArchive}
        &nbsp;&nbsp;&nbsp;| {archive, ZipFiles, ZipOptions}</v>
        <v>SourceCode = BeamCode = file:filename() | binary()</v>
        <v>ZipArchive = <seealso marker="stdlib:zip#type-filename">
          zip:filename()</seealso> | binary()</v>
        <v>ZipFiles = [ZipFile]</v>
        <v>ZipFile = file:filename()
        &nbsp;&nbsp;&nbsp;| {file:filename(), binary()}
        &nbsp;&nbsp;&nbsp;| {file:filename(), binary(), file:file_info()}</v>
        <v>ZipOptions = [<seealso marker="stdlib:zip#type-create_option">
          zip:create_option()</seealso>]</v>
      </type>
      <desc>
        <p><marker id="create_2"></marker>
          Creates an escript from a list of sections. The
          sections can be specified in any order. An escript begins with an
          optional <c>Header</c> followed by a mandatory <c>Body</c>. If
          the header is present, it does always begin with a
          <c>shebang</c>, possibly followed by a <c>comment</c> and
          <c>emu_args</c>. The <c>shebang</c> defaults to
          <c>"/usr/bin/env escript"</c>. The <c>comment</c> defaults to
          <c>"This is an -*- erlang -*- file"</c>. The created escript
          can either be returned as a binary or written to file.</p>
        <p>As an example of how the function can be used, we create an
          interpreted escript that uses <c>emu_args</c> to set some emulator
          flag. In this case, it happens to disable the <c>smp_support</c>. We
          also extract the different sections from the newly created script:</p>
        <pre>
&gt; <input>Source = "%% Demo\nmain(_Args) ->\n    io:format(erlang:system_info(smp_support)).\n".</input>
"%% Demo\nmain(_Args) ->\n    io:format(erlang:system_info(smp_support)).\n"
&gt; <input>io:format("~s\n", [Source]).</input>
%% Demo
main(_Args) ->
    io:format(erlang:system_info(smp_support)).

ok
&gt; <input>{ok, Bin} = escript:create(binary, [shebang, comment, {emu_args, "-smp disable"},
                                      {source, list_to_binary(Source)}]).</input>
{ok,&lt;&lt;"#!/usr/bin/env escript\n%% This is an -*- erlang -*- file\n%%!-smp disabl"...&gt;&gt;}
&gt; <input>file:write_file("demo.escript", Bin).</input>
ok
&gt; <input>os:cmd("escript demo.escript").</input>
"false"
&gt; <input>escript:extract("demo.escript", []).</input>
{ok,[{shebang,default}, {comment,default}, {emu_args,"-smp disable"},
     {source,&lt;&lt;"%% Demo\nmain(_Args) ->\n    io:format(erlang:system_info(smp_su"...&gt;&gt;}]}</pre>
        <p>An escript without header can be created as follows:</p>
        <pre>
&gt; <input>file:write_file("demo.erl",
                  ["%% demo.erl\n-module(demo).\n-export([main/1]).\n\n", Source]).</input>
ok
&gt; <input>{ok, _, BeamCode} = compile:file("demo.erl", [binary, debug_info]).</input>
{ok,demo,
    &lt;&lt;70,79,82,49,0,0,2,208,66,69,65,77,65,116,111,109,0,0,0,
      79,0,0,0,9,4,100,...&gt;&gt;}
&gt; <input>escript:create("demo.beam", [{beam, BeamCode}]).</input>
ok
&gt; <input>escript:extract("demo.beam", []).</input>
{ok,[{shebang,undefined}, {comment,undefined}, {emu_args,undefined},
     {beam,&lt;&lt;70,79,82,49,0,0,3,68,66,69,65,77,65,116,
             111,109,0,0,0,83,0,0,0,9,...&gt;&gt;}]}
&gt; <input>os:cmd("escript demo.beam").</input>
"true"</pre>
        <p>Here we create an archive script containing both Erlang
          code and Beam code, then we iterate over all files in
          the archive and collect their contents and some information about
          them:</p>
        <pre>
&gt; <input>{ok, SourceCode} = file:read_file("demo.erl").</input>
{ok,&lt;&lt;"%% demo.erl\n-module(demo).\n-export([main/1]).\n\n%% Demo\nmain(_Arg"...&gt;&gt;}
&gt; <input>escript:create("demo.escript",
                 [shebang,
                  {archive, [{"demo.erl", SourceCode},
                             {"demo.beam", BeamCode}], []}]).</input>
ok
&gt; <input>{ok, [{shebang,default}, {comment,undefined}, {emu_args,undefined},
     {archive, ArchiveBin}]} = escript:extract("demo.escript", []).</input>
{ok,[{shebang,default}, {comment,undefined}, {emu_args,undefined},
     {{archive,&lt;&lt;80,75,3,4,20,0,0,0,8,0,118,7,98,60,105,
                152,61,93,107,0,0,0,118,0,...&gt;&gt;}]}
&gt; <input>file:write_file("demo.zip", ArchiveBin).</input>
ok
&gt; <input>zip:foldl(fun(N, I, B, A) -> [{N, I(), B()} | A] end, [], "demo.zip").</input>
{ok,[{"demo.beam",
      {file_info,748,regular,read_write,
                 {{2010,3,2},{0,59,22}},
                 {{2010,3,2},{0,59,22}},
                 {{2010,3,2},{0,59,22}},
                 54,1,0,0,0,0,0},
      &lt;&lt;70,79,82,49,0,0,2,228,66,69,65,77,65,116,111,109,0,0,0,
        83,0,0,...&gt;&gt;},
     {"demo.erl",
      {file_info,118,regular,read_write,
                 {{2010,3,2},{0,59,22}},
                 {{2010,3,2},{0,59,22}},
                 {{2010,3,2},{0,59,22}},
                 54,1,0,0,0,0,0},
      &lt;&lt;"%% demo.erl\n-module(demo).\n-export([main/1]).\n\n%% Demo\nmain(_Arg"...&gt;&gt;}]}</pre>
      </desc>
    </func>

    <func>
      <name>escript:extract(File, Options) -> {ok, Sections} |
        {error, term()}</name>
      <fsummary>Parse an escript and extract its sections.</fsummary>
      <type>
        <v>File = filename()</v>
        <v>Options = [] | [compile_source]</v>
        <v>Sections = Headers Body</v>
        <v>Headers =  {shebang, Shebang}
          {comment, Comment}
          {emu_args, EmuArgs}</v>
        <v>Shebang = string() | 'default' | 'undefined'</v>
        <v>Comment = string() | 'default' | 'undefined'</v>
        <v>EmuArgs = string() | 'undefined'</v>
        <v>Body = {source, SourceCode}
        &nbsp;&nbsp;&nbsp;| {source, BeamCode}
        &nbsp;&nbsp;&nbsp;| {beam, BeamCode}
        &nbsp;&nbsp;&nbsp;| {archive, ZipArchive}</v>
        <v>SourceCode = BeamCode = ZipArchive = binary()</v>
      </type>
      <desc>
        <p><marker id="extract_2"></marker>
          Parses an escript and extracts its sections. This is the reverse
          of <seealso marker="#create_2"><c>create/2</c></seealso>.</p>
        <p>All sections are returned even if they do not exist in the
          escript. If a particular section happens to have the same
          value as the default value, the extracted value is set to the
          atom <c>default</c>. If a section is missing, the extracted
          value is set to the atom <c>undefined</c>.</p>
        <p>Option <c>compile_source</c> only affects the result if
          the escript contains <c>source</c> code. In this case the
          Erlang code is automatically compiled and <c>{source,
          BeamCode}</c> is returned instead of <c>{source,
          SourceCode}</c>.</p>
        <p>Example:</p>
        <pre>
&gt; <input>escript:create("demo.escript",
                 [shebang, {archive, [{"demo.erl", SourceCode},
                                      {"demo.beam", BeamCode}], []}]).</input>
ok
&gt; <input>{ok, [{shebang,default}, {comment,undefined}, {emu_args,undefined},
     {archive, ArchiveBin}]} =
              escript:extract("demo.escript", []).</input>
{ok,[{{archive,&lt;&lt;80,75,3,4,20,0,0,0,8,0,118,7,98,60,105,
                152,61,93,107,0,0,0,118,0,...&gt;&gt;}
     {emu_args,undefined}]}</pre>
      </desc>
    </func>

    <func>
      <name>escript:script_name() -> File</name>
      <fsummary>Return the name of an escript.</fsummary>
      <type>
        <v>File = filename()</v>
      </type>
      <desc>
        <p><marker id="script_name_0"></marker>
          Returns the name of the escript that is executed.
          If the function is invoked outside the context
          of an escript, the behavior is undefined.</p>
      </desc>
    </func>
  </funcs>

  <section>
    <title>Options Accepted By escript</title>
    <taglist>
      <tag><c>-c</c></tag>
      <item>Compiles the escript regardless of the value of the mode attribute.
      </item>
      <tag><c>-d</c></tag>
      <item>Debugs the escript. Starts the debugger, loads the module
        containing the <c>main/1</c> function into the debugger, sets a
        breakpoint in <c>main/1</c>, and invokes <c>main/1</c>. If the
        module is precompiled, it must be explicitly compiled with option
        <c>debug_info</c>.
      </item>
      <tag><c>-i</c></tag>
      <item>Interprets the escript regardless of the value of the mode
        attribute.
      </item>
      <tag><c>-s</c></tag>
      <item>Performs a syntactic and semantic check of the script file.
        Warnings and errors (if any) are written to the standard output, but
        the script will not be run. The exit status is <c>0</c> if any errors
        are found, otherwise <c>127</c>.
      </item>
      <tag><c>-n</c></tag>
      <item>Compiles the escript using flag <c>+native</c>.
      </item>
    </taglist>
  </section>
</comref>