Modulinos

It is useful to be able to execute a main() function only when a program is run directly. This is a central feature in programming scripts; the feature is called scripted main.

Examples from GitHub.

C

C programs have scripted main by default; as long as main() is not included in the header file, this program's (empty) API is accessible by other C code.

<lang c>#include "scriptedmain.h"

include <stdio.h>
include <unistd.h>

int main(int argc, char **argv) { char cwd[1024]; getcwd(cwd, sizeof(cwd));

printf("Directory: %s\n", cwd);

printf("Program: %s\n", argv[0]);

printf("Number of Args: %d\n", argc);

int i; for (i = 0; i < argc; i++) { printf("Arg: %s\n", argv[i]); }

return 0; }</lang>

C++

C++ has scripted main by default.

<lang cpp>#include <iostream>

include <unistd.h>

using namespace std;

int main(int argc, char **argv) { char cwd[1024]; getcwd(cwd, sizeof(cwd));

cout << "Directory: " << cwd << endl;

cout << "Program: " << argv[0] << endl;

cout << "Number of Args: " << argc << endl;

int i; for (i = 0; i < argc; i++) { cout << "Arg: " << argv[i] << endl; }

return 0; }</lang>

Common Lisp

Common Lisp has few standards for POSIX operation. Shebangs and command line arguments are hacks.

In CLISP, this code only works for ./scriptedmain.lisp.

<lang lisp>#!/bin/bash

|

exec clisp -q -q $0 $0 ${1+"$@"} exit |#

Usage

./scriptedmain.lisp

With help from Rainer Joswig http://www.math.utexas.edu/pipermail/maxima/2007/006523.html

(defun main (args)

(format t "Directory: ~a~%"
 #+clisp (ext:cd)
 #+lucid (working-directory)
 #+allegro (excl:current-directory)
 #+sbcl (progn *default-pathname-defaults*)
 #+(or :cmucl :scl) (ext:default-directory)
 #+lispworks (hcl:get-working-directory)
)

(format t "Program: ~a~%" (car args))

(format t "Number of Args: ~a~%" (length args))

(loop for arg in args do
 (format t "Arg: ~a~%" arg))
(quit))

With help from Francois-Rene Rideau http://tinyurl.com/cli-args

(let ((args

      #+clisp ext:*args*
      #+sbcl sb-ext:*posix-argv*
      #+clozure (ccl::command-line-arguments)
      #+gcl si:*command-args*
      #+ecl (loop for i from 0 below (si:argc) collect (si:argv i))
      #+cmu extensions:*command-line-strings*
      #+allegro (sys:command-line-arguments)
      #+lispworks sys:*line-arguments-list*
    ))

 (if (member (pathname-name *load-truename*)
             args
             :test #'(lambda (x y) (search x y :test #'equalp)))
   (main args)))</lang>

Erlang

Erlang has scripted main by default.

<lang erlang>-module(scriptedmain). -import(lists, [map/2]).

main(Args) -> io:format("Directory: ~s~n", [filename:absname("")]), io:format("Program: ~s~n", [?FILE]), io:format("Number of Args: ~w~n", [length(Args)]), map (fun(Arg) -> io:format("Arg: ~s~n", [Arg]) end, Args).</lang>

Haskell

Haskell has scripted main by default.

<lang haskell>#!/usr/bin/env runhaskell

module ScriptedMain where

import System.Directory (getCurrentDirectory) import System (getProgName, getArgs) import Control.Monad (mapM_)

main :: IO () main = do directory <- getCurrentDirectory program <- getProgName args <- getArgs

putStrLn $ "Directory: " ++ directory putStrLn $ "Program: " ++ program putStrLn $ "Number of Args: " ++ (show . length) args mapM_ (\x -> putStrLn $ "Arg: " ++ x) args</lang>

Java

Java has scripted main by default.

<lang java>public class ScriptedMain { public static void main(String[] args) { System.out.println("Directory: " + ScriptedMain.class.getProtectionDomain().getCodeSource().getLocation().getPath());

System.out.println("Program: " + ScriptedMain.class.getName());

System.out.println("Number of Args: " + args.length);

for (int i = 0; i < args.length; i++) { System.out.println("Arg: " + args[i]); } } }</lang>

Lua

Lua has scripted main by default, using an obscure syntax (an ellipsis of all things).

<lang lua>#!/usr/bin/env lua

os = require("os")

function main(arg) print("Directory: " .. os.execute("pwd"))

print("Program: " .. debug.getinfo(1).source)

print("Number of Args: " .. #arg)

for i,a in ipairs(arg) do print("Arg: " .. a) end

end

if type(package.loaded[(...)]) ~= "userdata" then main(arg) else module(..., package.seeall) end</lang>

newLISP

newLISP lacks scripted main, but the feature is easily added.

<lang lisp>#!/usr/bin/env newlisp

(context 'SCRIPTED-MAIN)

(define (main) (println "Directory: " (real-path))

(println "Program: " (main-args 1))

(println "Number of Args: " (length (main-args)))

(map (lambda (x) (println "Arg: " x)) (main-args))

(exit))

(if (find "scriptedmain" (main-args 1)) (main))

(context MAIN)</lang>

Octave/MATLAB

Octave and MATLAB have scripted main by default, because only the first function listed in a program are importable by other programs. The scriptedmain() function is just filler.

<lang matlab>#!/usr/bin/env octave -qf

function scriptedmain() endfunction

function main() printf("Directory: %s\n", pwd()); printf("Program: %s\n", program_name()); printf("Number of Args: %d\n", nargin);

args = argv();

for i = 1:nargin printf("Arg: %s\n", args{i}); endfor

endfunction

main();</lang>

Perl

Perl has scripted main.

<lang perl>#!/usr/bin/env perl

use strict; use Cwd qw(getcwd);

sub main { print "Dirctory: " . getcwd . "\n";

print "Program: $0\n";

print "Number of Args: " . ($#ARGV + 1) . "\n";

foreach my $i (0 .. $#ARGV) { print "Arg: $ARGV[$i]\n"; } }

unless(caller) { main; }</lang>

PHP

PHP does not have scripted main, but the feature is easily added with a regular expression.

<lang php><?php function main($args) { echo "Directory: " . getcwd() . "\n";

echo "Program: " . $_SERVER["SCRIPT_NAME"] . "\n";

echo "Number of Args: " . count($args) . "\n";

foreach($args as $arg) { echo "Arg: $arg\n"; } }

if (preg_match("/scriptedmain/", $_SERVER["SCRIPT_NAME"])) { main($argv); } ?></lang>

Python

Python has scripted main.

<lang python>#!/usr/bin/env python

import os, sys

def main(): print "Directory: " + os.getcwd()

print "Program: " + sys.argv[0]

print "Number of Args: %d" % len(sys.argv)

for arg in sys.argv: print "Arg: " + arg

if __name__=="__main__": main()</lang>

Ruby

Ruby has scripted main by default.

<lang ruby>#!/usr/bin/env ruby

def main puts "Directory: #{Dir.pwd}"

puts "Program: #{$0}"

puts "Number of Args: #{ARGV.length}"

ARGV.each { |arg| puts "Arg: #{arg}" } end

if __FILE__ == $0 main end</lang>

UNIX Shell

Bash has scripted main.

<lang sh>#!/usr/bin/env sh

main() { echo "Directory: " `pwd`

echo "Program: $0"

echo "Number of Args: $#"

for arg in $*; do echo "Arg: $arg" done }

From Dennis Williamson
http://stackoverflow.com/questions/2683279/#2687092

if $_ == $0 ; then main fi</lang>