escript
(1)
Name
escript - Erlang scripting support
Synopsis
Please see following description for synopsis
Description
User Commands escript(1)
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.
$ 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. How-
ever if you invoke the escript like this
$ escript factorial 5
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User Commands escript(1)
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.
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 emula-
tor.
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 inter-
preted in any way).
If the main/1 function in the script returns success-
fully, the exit status for the script will be 0. If an
exception is generated during execution, a short mes-
sage will be printed and the script terminated with
exit status 127.
To return your own non-zero exit code, call halt(Exit-
Code); for instance:
halt(1).
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User Commands escript(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.
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 inter-
preted 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 com-
pile, 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 func-
tion 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
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User Commands escript(1)
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 %%! men-
tioned 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(3) 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}
SourceCode = BeamCode = ZipArchive = binary()
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
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User Commands escript(1)
either be returned as a binary or written to file.
As an example of how the function can be used, we cre-
ate 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 sec-
tions 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"...>>}
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User Commands escript(1)
> 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 miss-
ing, the extracted value is set to the atom undefined.
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User Commands escript(1)
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 out-
side the context of an escript, the behavior is unde-
fined.
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.
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User Commands escript(1)
ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | runtime/erlang |
+---------------+------------------+
|Stability | Uncommitted |
+---------------+------------------+
NOTES
This software was built from source available at
https://java.net/projects/solaris-userland. The original
community source was downloaded from
http://www.erlang.org/download/otp_src_R15B03-1.tar.gz
Further information about this software can be found on the
open source community website at http://www.erlang.org/.
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