<?xml version="1.0" encoding="utf-8" ?> <!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 limitations under the License. </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} | comment | {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} | {beam, BeamCode} | {archive, ZipArchive} | {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() | {file:filename(), binary()} | {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> > <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" > <input>io:format("~s\n", [Source]).</input> %% Demo main(_Args) -> io:format(erlang:system_info(smp_support)). ok > <input>{ok, Bin} = escript:create(binary, [shebang, comment, {emu_args, "-smp disable"}, {source, list_to_binary(Source)}]).</input> {ok,<<"#!/usr/bin/env escript\n%% This is an -*- erlang -*- file\n%%!-smp disabl"...>>} > <input>file:write_file("demo.escript", Bin).</input> ok > <input>os:cmd("escript demo.escript").</input> "false" > <input>escript:extract("demo.escript", []).</input> {ok,[{shebang,default}, {comment,default}, {emu_args,"-smp disable"}, {source,<<"%% Demo\nmain(_Args) ->\n io:format(erlang:system_info(smp_su"...>>}]}</pre> <p>An escript without header can be created as follows:</p> <pre> > <input>file:write_file("demo.erl", ["%% demo.erl\n-module(demo).\n-export([main/1]).\n\n", Source]).</input> ok > <input>{ok, _, BeamCode} = compile:file("demo.erl", [binary, debug_info]).</input> {ok,demo, <<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,...>>} > <input>escript:create("demo.beam", [{beam, BeamCode}]).</input> ok > <input>escript:extract("demo.beam", []).</input> {ok,[{shebang,undefined}, {comment,undefined}, {emu_args,undefined}, {beam,<<70,79,82,49,0,0,3,68,66,69,65,77,65,116, 111,109,0,0,0,83,0,0,0,9,...>>}]} > <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> > <input>{ok, SourceCode} = file:read_file("demo.erl").</input> {ok,<<"%% demo.erl\n-module(demo).\n-export([main/1]).\n\n%% Demo\nmain(_Arg"...>>} > <input>escript:create("demo.escript", [shebang, {archive, [{"demo.erl", SourceCode}, {"demo.beam", BeamCode}], []}]).</input> ok > <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,<<80,75,3,4,20,0,0,0,8,0,118,7,98,60,105, 152,61,93,107,0,0,0,118,0,...>>}]} > <input>file:write_file("demo.zip", ArchiveBin).</input> ok > <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}, <<70,79,82,49,0,0,2,228,66,69,65,77,65,116,111,109,0,0,0, 83,0,0,...>>}, {"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}, <<"%% demo.erl\n-module(demo).\n-export([main/1]).\n\n%% Demo\nmain(_Arg"...>>}]}</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} | {source, BeamCode} | {beam, BeamCode} | {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> > <input>escript:create("demo.escript", [shebang, {archive, [{"demo.erl", SourceCode}, {"demo.beam", BeamCode}], []}]).</input> ok > <input>{ok, [{shebang,default}, {comment,undefined}, {emu_args,undefined}, {archive, ArchiveBin}]} = escript:extract("demo.escript", []).</input> {ok,[{{archive,<<80,75,3,4,20,0,0,0,8,0,118,7,98,60,105, 152,61,93,107,0,0,0,118,0,...>>} {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>