Provided by: erlang-base-hipe_18.3-dfsg-1ubuntu3.1_amd64 
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.