escript(1) User Commands escript(1)NAMEescript - Erlang scripting support
DESCRIPTIONescript provides support for running short Erlang programs without hav‐
ing 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 gener‐
ated 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 correct‐
ness 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 con‐
tains precompiled beam code. In a precompiled script, the inter‐
pretation 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 contain‐
ing 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 Mod‐
ule 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 sec‐
tions. 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 sec‐
tions. 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 automati‐
cally 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.
Ericsson AB erts 6.3 escript(1)
