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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.

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

       The  (built-in)  escript  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 escript program itself. But for standalone systems with one or
       more escripts it may be the case that the escript program in your path actually starts the
       runtime  system  bundled with the escript. This is intentional, and typically happens when
       the standalone system bin directory is not in the execution path (as it may cause its  erl
       program to override the desired one) and the escript(s) are referred to via symbolic links
       from a bin directory in the path.

EXPORTS

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

              escript runs a script written in Erlang.

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

              $ escript factorial 5

              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 a comment selecting the encoding exists, 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, must be set explicitly as follows:

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

              The  default  encoding  of  the I/O-server for standard_io is latin1, as the script
              runs in a non-interactive terminal (see section  Summary of Options) in the  STDLIB
              User's Guide.

              On  the  third  line  (or  second  line  depending  on  the  presence  of the Emacs
              directive), arguments can be specified to the emulator, for example:

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

              Such an argument line must start with %%! and the remaining line is 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 example:

              #!/usr/local/bin/escript

              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
              chmod +x script-name.)

              The remaining Erlang script file can either contain Erlang source code, an  inlined
              beam file, or an inlined archive file.

              An  Erlang  script file must always contain the main/1 function. When the script is
              run, the main/1 function  is  called  with  a  list  of  strings  representing  the
              arguments specified 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 is 0. If an exception is generated during  execution,  a  short  message  is
              printed and the script terminates with exit status 127.

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

              halt(1).

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

              If the file contains source code (as in the example above), it is processed by  the
              epp preprocessor. This means that you, for example, can use predefined macros (such
              as ?MODULE) and include directives like the -include_lib  directive.  For  example,
              use

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

              to   include   the   record   definitions   for   the   records  used  by  function
              file:read_link_info/1. 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.

              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 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 can  be  worthwhile  to  compile  it,
              although  the compilation itself takes a little while. Also, native can be supplied
              instead of compile. This compiles the script using the native flag and may  or  may
              not be worthwhile depending on the escript characteristics.

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

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

              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:

              $ 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()]

              Creates an escript from a list of sections. The sections can be  specified  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
              that uses emu_args to set some emulator flag. In this case, it happens  to  disable
              the  smp_support.  We  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 as follows:

              > 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 and Beam code, then we
              iterate  over  all  files  in  the  archive  and  collect  their  contents and some
              information 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()

              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.

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

              Example:

              > 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()

              Returns the name of the escript that  is  executed.  If  the  function  is  invoked
              outside the context of an escript, the behavior is undefined.

OPTIONS ACCEPTED BY ESCRIPT

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

         -d:
           Debugs  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 option debug_info.

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

         -s:
           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 0 if any errors are found, otherwise 127.

         -n:
           Compiles the escript using flag +native.