xenial (1) escript.1.gz

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NAME

       escript - Erlang scripting support

DESCRIPTION

       escript  provides  support  for running short Erlang programs without having to compile them first and an
       easy way to retrieve the command line arguments.

EXPORTS

       script-name script-arg1 script-arg2...
       escript escript-flags script-name script-arg1 script-arg2...

              escript runs a script written in Erlang.

              Here follows an example.

              $ chmod u+x factorial
              $ cat factorial
              #!/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).
              $ ./factorial 5
              factorial 5 = 120
              $ ./factorial
              usage: factorial integer
              $ ./factorial five
              usage: factorial integer

              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 escript. However if you invoke the escript
              like this

              $ escript factorial 5

              the contents of the first line does not matter, but it cannot contain Erlang code as  it  will  be
              ignored.

              The second line in the example, contains an optional directive to the Emacs 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.

              If there is a comment selecting the encoding it can be located on the second line.

          Note:
              The  encoding  specified by the above mentioned comment applies to the script itself. The encoding
              of the I/O-server, however, has to be set explicitly like this:

              io:setopts([{encoding, unicode}])

              The default encoding of the I/O-server for standard_io is latin1 since the script runs in  a  non-
              interactive terminal (see  Using Unicode in Erlang).

              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

              %%! -smp enable -sname factorial -mnesia debug verbose

              Such an argument line must start with %%! and the rest of the line will interpreted  as  arguments
              to the emulator.

              If  you  know the location of the escript executable, the first line can directly give the path to
              escript. For instance:

              #!/usr/local/bin/escript

              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 chmod +x script-name to turn on the execution bit.)

              The  rest of the Erlang script file may either contain Erlang source code, an inlined beam file or
              an inlined archive file.

              An Erlang script file must always contain the function main/1. When the script is run, the  main/1
              function will be called with a list of strings representing the arguments given to the script (not
              changed or interpreted in any way).

              If the main/1 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.

              To return your own non-zero exit code, call halt(ExitCode); for instance:

              halt(1).

              Call escript:script_name() from your to script  to  retrieve  the  pathname  of  the  script  (the
              pathname is usually, but not always, absolute).

              If  the  file  contains  source  code  (as  in  the  example  above),  it will be processed by the
              preprocessor epp. This means that you for example may use pre-defined macros (such as ?MODULE)  as
              well as include directives like the -include_lib directive. For instance, use

              -include_lib("kernel/include/file.hrl").

              to  include the record definitions for the records used by the file:read_link_info/1 function. You
              can also select encoding by including a encoding comment here, but if there is  a  valid  encoding
              comment on the second line it takes precedence.

              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.

              Both the module declaration and the export declaration of the main/1 function are optional.

              By default, the script will be interpreted. You can force it  to  be  compiled  by  including  the
              following line somewhere in the script file:

              -mode(compile).

              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. It is also possible to supply native instead of compile, this will compile
              the script using the native flag, again depending on the characteristics of the escript this could
              or could not be worth while.

              As  mentioned  earlier, it is possible to have a script which contains precompiled beam 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 beam file executable by prepending the file
              with the lines starting with #! and %%! mentioned above. In a  precompiled  script,  the  function
              main/1 must be exported.

              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 #! and %%! mentioned above. In an archive script, the function main/1 must
              be  exported.  By  default the main/1 function in the module with the same name as the basename of
              the escript file will be invoked. This behavior can be overridden by  setting  the  flag  -escript
              main  Module  as  one  of the emulator flags. The Module must be the name of a module which has an
              exported main/1 function. See code(3erl) for more information about archives and code loading.

              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:

              $ escript factorial.erl 5
              factorial 5 = 120
              $ escript factorial.beam 5
              factorial 5 = 120
              $ escript factorial.zip 5
              factorial 5 = 120

       escript:create(FileOrBin, Sections) -> ok | {ok, binary()} | {error, term()}

              Types:

                 FileOrBin = filename() | 'binary'
                 Sections = [Header] Body | Body
                 Header = shebang | {shebang, Shebang} | comment | {comment, Comment} | {emu_args, EmuArgs}
                 Shebang = string() | 'default' | 'undefined'
                 Comment = string() | 'default' | 'undefined'
                 EmuArgs = string() | 'undefined'
                 Body  =  {source,  SourceCode} | {beam, BeamCode} | {archive, ZipArchive} | {archive, ZipFiles,
                 ZipOptions}
                 SourceCode = BeamCode = file:filename() | binary()
                 ZipArchive = zip:filename() | binary()
                 ZipFiles = [ZipFile]
                 ZipFile  =  file:filename()  |  {file:filename(),  binary()}  |   {file:filename(),   binary(),
                 file:file_info()}
                 ZipOptions = [zip:create_option()]

              The create/2 function creates an escript from a list of sections. The sections can be given in any
              order. An escript begins with an optional Header followed by a mandatory Body. If  the  header  is
              present,  it  does  always  begin with a shebang, possibly followed by a comment and emu_args. The
              shebang defaults to "/usr/bin/env escript". The comment defaults to "This is  an  -*-  erlang  -*-
              file". The created escript can either be returned as a binary or written to file.

              As  an  example  of  how  the  function  can  be used, we create an interpreted escript which uses
              emu_args to set some emulator flag. In this case it happens to disable the smp_support. We do also
              extract the different sections from the newly created script:

              > Source = "%% Demo\nmain(_Args) ->\n io:format(erlang:system_info(smp_support)).\n".
              "%% Demo\nmain(_Args) ->\n    io:format(erlang:system_info(smp_support)).\n"
              > io:format("~s\n", [Source]).
              %% Demo
              main(_Args) ->
                  io:format(erlang:system_info(smp_support)).

              ok
              > {ok, Bin} = escript:create(binary, [shebang, comment, {emu_args, "-smp disable"}, {source, list_to_binary(Source)}]).
              {ok,<<"#!/usr/bin/env escript\n%% This is an -*- erlang -*- file\n%%!-smp disabl"...>>}
              > file:write_file("demo.escript", Bin).
              ok
              > os:cmd("escript demo.escript").
              "false"
              > escript:extract("demo.escript", []).
              {ok,[{shebang,default}, {comment,default}, {emu_args,"-smp disable"},
                   {source,<<"%% Demo\nmain(_Args) ->\n    io:format(erlang:system_info(smp_su"...>>}]}

              An escript without header can be created like this:

              > file:write_file("demo.erl", ["%% demo.erl\n-module(demo).\n-export([main/1]).\n\n", Source]).
              ok
              > {ok, _, BeamCode} = compile:file("demo.erl", [binary, debug_info]).
              {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,...>>}
              > escript:create("demo.beam", [{beam, BeamCode}]).
              ok
              > escript:extract("demo.beam", []).
              {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,...>>}]}
              > os:cmd("escript demo.beam").
              "true"

              Here we create an archive script containing both Erlang code as well as beam code. Then we iterate
              over all files in the archive and collect their contents and some info about them.

              > {ok, SourceCode} = file:read_file("demo.erl").
              {ok,<<"%% demo.erl\n-module(demo).\n-export([main/1]).\n\n%% Demo\nmain(_Arg"...>>}
              > escript:create("demo.escript", [shebang, {archive, [{"demo.erl", SourceCode}, {"demo.beam", BeamCode}], []}]).
              ok
              > {ok, [{shebang,default}, {comment,undefined}, {emu_args,undefined}, {archive, ArchiveBin}]} = escript:extract("demo.escript", []).
              {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,...>>}]}
              > file:write_file("demo.zip", ArchiveBin).
              ok
              > zip:foldl(fun(N, I, B, A) -> [{N, I(), B()} | A] end, [], "demo.zip").
              {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"...>>}]}

       escript:extract(File, Options) -> {ok, Sections} | {error, term()}

              Types:

                 File = filename()
                 Options = [] | [compile_source]
                 Sections = Headers Body
                 Headers = {shebang, Shebang} {comment, Comment} {emu_args, EmuArgs}
                 Shebang = string() | 'default' | 'undefined'
                 Comment = string() | 'default' | 'undefined'
                 EmuArgs = string() | 'undefined'
                 Body = {source, SourceCode} | {source, BeamCode} | {beam, BeamCode} | {archive, ZipArchive}
                 SourceCode = BeamCode = ZipArchive = binary()

              The extract/2 function parses an escript and  extracts  its  sections.  This  is  the  reverse  of
              create/2.

              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
              default. If a section is missing, the extracted value is set to the atom undefined.

              The  compile_source  option  only  affects the result if the escript contains source code. In that
              case the Erlang code is automatically compiled and  {source,  BeamCode}  is  returned  instead  of
              {source, SourceCode}.

              > escript:create("demo.escript", [shebang, {archive, [{"demo.erl", SourceCode}, {"demo.beam", BeamCode}], []}]).
              ok
              > {ok, [{shebang,default}, {comment,undefined}, {emu_args,undefined}, {archive, ArchiveBin}]} = escript:extract("demo.escript", []).
              {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}]}

       escript:script_name() -> File

              Types:

                 File = filename()

              The  script_name/0  function  returns  the  name of the escript being executed. If the function is
              invoked outside the context of an escript, the behavior is undefined.

OPTIONS ACCEPTED BY ESCRIPT

         -c:
           Compile the escript regardless of the value of the mode attribute.

         -d:
           Debug the escript. Starts the debugger, loads the module containing  the  main/1  function  into  the
           debugger,  sets  a  breakpoint in main/1 and invokes main/1. If the module is precompiled, it must be
           explicitly compiled with the debug_info option.

         -i:
           Interpret the escript regardless of the value of the mode attribute.

         -s:
           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.

         -n:
           Compile the escript using the +native flag.