<?xml version="1.0" encoding="latin1" ?> <!DOCTYPE comref SYSTEM "comref.dtd"> <comref> <header> <copyright> <year>2007</year><year>2009</year> <holder>Ericsson AB. All Rights Reserved.</holder> </copyright> <legalnotice> The contents of this file are subject to the Erlang Public License, Version 1.1, (the "License"); you may not use this file except in compliance with the License. You should have received a copy of the Erlang Public License along with this software. If not, it can be retrieved online at http://www.erlang.org/. Software distributed under the License is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License for the specific language governing rights 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><![CDATA[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> </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><![CDATA[escript]]></c> runs a script written in Erlang.</p> <p>Here follows an example.</p> <pre> $ <input>cat factorial</input> #!/usr/bin/env escript %% -*- erlang -*- %%! -smp enable -sname factorial -mnesia debug verbose main([String]) -> try \011N = list_to_integer(String), \011F = fac(N), \011io:format("factorial ~w = ~w\ ", [N,F]) catch \011_:_ -> \011 usage() end; main(_) -> usage(). usage() -> io:format("usage: factorial integer\ "), 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><![CDATA[escript]]></c>. However if you invoke the <c><![CDATA[escript]]></c> like this</p> <pre> $ <input>escript factorial 5</input> </pre> <p>the contents of the first line does not matter, but it cannot contain Erlang code as it will be ignored.</p> <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>On the third line (or second line depending on the presence of the Emacs directive), it is possible to give arguments to the emulator, such as </p> <pre> %%! -smp enable -sname factorial -mnesia debug verbose</pre> <p>Such an argument line must start with <c>%%!</c> and the rest of the line will interpreted as arguments to the emulator.</p> <p>If you know the location of the <c><![CDATA[escript]]></c> executable, the first line can directly give the path to <c><![CDATA[escript]]></c>. For instance:</p> <pre> #!/usr/local/bin/escript </pre> <p>As any other kind of scripts, Erlang scripts will not work on Unix platforms if the execution bit for the script file is not set. (Use <c><![CDATA[chmod +x script-name]]></c> to turn on the execution bit.) </p> <p>The rest of the Erlang script file may either contain Erlang <c>source code</c>, an <c>inlined beam file</c> or an <c>inlined archive file</c>.</p> <p>An Erlang script file must always contain the function <em>main/1</em>. When the script is run, the <c><![CDATA[main/1]]></c> function will be called with a list of strings representing the arguments given to the script (not changed or interpreted in any way).</p> <p>If the <c><![CDATA[main/1]]></c> function in the script returns successfully, the exit status for the script will be 0. If an exception is generated during execution, a short message will be printed and the script terminated with exit status 127.</p> <p>To return your own non-zero exit code, call <c><![CDATA[halt(ExitCode)]]></c>; for instance:</p> <pre> halt(1).</pre> <p>Call <c><![CDATA[escript:script_name/0]]></c> from your to script to retrieve the pathname of the script (the pathname is usually, but not always, absolute).</p> <p>If the file contains source code (as in the example above), it will be processed by the preprocessor <c>epp</c>. This means that you for example may use pre-defined macros (such as <c><![CDATA[?MODULE]]></c>) as well as include directives like the <c><![CDATA[-include_lib]]></c> directive. For instance, use</p> <pre> -include_lib("kernel/include/file.hrl"). </pre> <p>to include the record definitions for the records used by the <c><![CDATA[file:read_link_info/1]]></c> function.</p> <p>The script will be checked for syntactic and semantic correctness before being run. If there are warnings (such as unused variables), they will be printed and the script will still be run. If there are errors, they will be printed and the script will not be run and its exit status will be 127.</p> <p>Both the module declaration and the export declaration of the <c><![CDATA[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 may be worthwhile to compile it, even though the compilation itself will take a little while.</p> <p>As mentioned earlier, it is possible to have a script which contains precompiled <c>beam</c> code. In a precompiled script, the interpretation of the script header is exactly the same as in a script containing source code. That 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 function <c>main/1</c> must be exported.</p> <p>As yet another option it is possible to have an entire Erlang archive in the script. In a archive script, the interpretation of the script header is exactly the same as in a script containing source code. That 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 function <c>main/1</c> 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 will be invoked. This behavior can be overridden by setting the flag <c>-escript main Module</c> as one of the emulator flags. The <c>Module</c> must be the name of a module which has an exported <c>main/1</c> function. See <seealso marker="kernel:code">code(3)</seealso> for more information about archives and code loading.</p> <p>In many cases it is very convenient to have a header in the escript, especially on Unix platforms. But the header is in fact optional. This means that 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 like this:</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> </funcs> <section> <title>Options accepted by escript</title> <taglist> <tag>-c</tag> <item>Compile the escript regardless of the value of the mode attribute. </item> <tag>-d</tag> <item>Debug 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 the <c>debug_info</c> option. </item> <tag>-i</tag> <item>Interpret the escript regardless of the value of the mode attribute. </item> <tag>-s</tag> <item>Only perform 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 will be 0 if there were no errors, and 127 otherwise.</item> </taglist> </section> </comref>