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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 can be called scripted main or modulino.

Examples from GitHub.

Sometimes getting the ScriptName is required in order to determine when to run main().

This is still a draft task, and the current task description has caused mega confusion. See Talk:Scripted Main for numerous attempts to understand the task and to rewrite the task description.

The task Executable library is written to replace this task. This task's future is in doubt as its aims are not clear enough.

C

Works with: GCC

C programs cannot normally do scripted main, because main() is implicitly included by another program, test.c, even though scriptedmain.h omits any main() prototype. However, preprocessor instructions can hide main unless a compiler flag is explicitly set.

Example

<lang sh>$ make ./scriptedmain Main: The meaning of life is 42 ./test Test: The meaning of life is</lang>

Makefile

<lang make>all: scriptedmain test ./scriptedmain ./test

scriptedmain: scriptedmain.c scriptedmain.h gcc -o scriptedmain -DSCRIPTEDMAIN scriptedmain.c scriptedmain.h

test: test.c scriptedmain.h scriptedmain.c gcc -o test test.c scriptedmain.c scriptedmain.h

clean: -rm scriptedmain -rm test -rm scriptedmain.exe -rm test.exe</lang>

scriptedmain.h

<lang c>int meaning_of_life();</lang>

scriptedmain.c

<lang c>#include <stdio.h>

int meaning_of_life() { return 42; }

ifdef SCRIPTEDMAIN

int main() { printf("Main: The meaning of life is %d\n", meaning_of_life());

return 0; }

endif</lang>

test.c

<lang c>#include "scriptedmain.h"

include <stdio.h>

extern int meaning_of_life();

int main(int argc, char **argv) { printf("Test: The meaning of life is %d\n", meaning_of_life()); return 0; }</lang>

C++

C++ programs cannot normally do scripted main, because main() is implicitly included by another program, test.c, even though scriptedmain.h omits any main() prototype. Preprocessor instructions can hide main() unless a compiler flat is explicitly set.

Example

<lang sh>$ make ./scriptedmain Main: The meaning of life is 42 ./test Test: The meaning of life is 42</lang>

Makefile

<lang make>all: scriptedmain test ./scriptedmain ./test

scriptedmain: scriptedmain.cpp scriptedmain.h g++ -o scriptedmain -static-libgcc -static-libstdc++ -DSCRIPTEDMAIN scriptedmain.cpp scriptedmain.h

test: test.cpp scriptedmain.h scriptedmain.cpp g++ -o test -static-libgcc -static-libstdc++ test.cpp scriptedmain.cpp scriptedmain.h

clean: -rm scriptedmain -rm test -rm scriptedmain.exe -rm test.exe</lang>

scriptedmain.h

<lang cpp>int meaning_of_life();</lang>

scriptedmain.cpp

<lang cpp>#include <iostream>

using namespace std;

int meaning_of_life() { return 42; }

ifdef SCRIPTEDMAIN

int main() { cout << "Main: The meaning of life is " << meaning_of_life() << endl; return 0; }

endif</lang>

test.cpp

<lang cpp>#include "scriptedmain.h"

include <iostream>

using namespace std;

extern int meaning_of_life();

int main() { cout << "Test: The meaning of life is " << meaning_of_life() << endl; return 0; }</lang>

Chicken Scheme

Chicken Scheme has the {{{ -ss }}} flag for the interpreter, but compiled Chicken Scheme programs do not have scripted main unless the behavior is added manually to the code.

scriptedmain.scm

<lang scheme>#!/bin/sh

|

exec csi -ss $0 ${1+"$@"} exit |#

(use posix) (require-extension srfi-1) ; lists

(define (meaning-of-life) 42)

(define (main args) (display (format "Main: The meaning of life is ~a\n" (meaning-of-life))) (exit))

(define (program) (if (string=? (car (argv)) "csi") (let ((s-index (list-index (lambda (x) (string-contains x "-s")) (argv)))) (if (number? s-index) (cons 'interpreted (list-ref (argv) (+ 1 s-index))) (cons 'unknown ""))) (cons 'compiled (car (argv)))))

(if (equal? (car (program)) 'compiled) (main (cdr (argv))))</lang>

test.scm

<lang scheme>#!/bin/sh

|

exec csi -ss $0 ${1+"$@"} exit |# (define (main args) (load "scriptedmain.scm") (display (format "Test: The meaning of life is ~a\n" (meaning-of-life))) (exit))</lang>

Clojure

Uses lein-exec.

scriptedmain.clj: <lang clojure>":";exec lein exec $0 ${1+"$@"} ":";exit

(ns scriptedmain

 (:gen-class))

(defn meaning-of-life [] 42)

(defn -main [& args]

 (println "Main: The meaning of life is" (meaning-of-life)))

(when (.contains (first *command-line-args*) *source-path*)

 (apply -main (rest *command-line-args*)))</lang>

test.clj: <lang clojure>":";exec lein exec $0 ${1+"$@"} ":";exit

(ns test

 (:gen-class))

(load-string (slurp "scriptedmain.clj"))

(defn -main [& args]

 (println "Test: The meaning of life is" (scriptedmain/meaning-of-life)))

(when (.contains (first *command-line-args*) *source-path*)

 (apply -main (rest *command-line-args*)))</lang>

Coffeescript

scriptedmain.coffee: <lang coffeescript>#!/usr/bin/env coffee

meaningOfLife = () -> 42

exports.meaningOfLife = meaningOfLife

main = () ->

 console.log "Main: The meaning of life is " + meaningOfLife()

if not module.parent then main()</lang>

test.coffee: <lang coffeescript>#!/usr/bin/env coffee

sm = require "./scriptedmain"

console.log "Test: The meaning of life is " + sm.meaningOfLife()</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.

~/.clisprc.lisp

<lang lisp>;;; Play nice with shebangs (set-dispatch-macro-character #\# #\!

(lambda (stream character n)
 (declare (ignore character n))
 (read-line stream nil nil t)
 nil))</lang>

scriptedmain.lisp

<lang lisp>#!/bin/sh

|

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

Usage

./scriptedmain.lisp

(defun meaning-of-life () 42)

(defun main (args)

(format t "Main: The meaning of life is ~a~%" (meaning-of-life))
(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>

test.lisp

<lang lisp>#!/bin/sh

|

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

(load "scriptedmain.lisp") (format t "Test: The meaning of life is ~a~%" (meaning-of-life))</lang>

D

D manages to implement scriptedmain through the use of version directives, which require special options to rdmd and dmd.

scriptedmain.d:

<lang d>#!/usr/bin/env rdmd -version=scriptedmain

module scriptedmain;

import std.stdio;

int meaningOfLife() { return 42; }

version (scriptedmain) { void main(string[] args) { writeln("Main: The meaning of life is ", meaningOfLife()); } }</lang>

test.d:

<lang d>#!/usr/bin/env rdmd -version=test

import scriptedmain; import std.stdio;

version (test) { void main(string[] args) { writeln("Test: The meaning of life is ", meaningOfLife()); } }</lang>

Example:

<lang sh>$ ./scriptedmain.d Main: The meaning of life is 42 $ ./test.d Test: The meaning of life is 42 $ dmd scriptedmain.d -version=scriptedmain $ ./scriptedmain Main: The meaning of life is 42 $ dmd test.d scriptedmain.d -version=test $ ./test Test: The meaning of life is 42</lang>

Dart

scriptedmain.dart: <lang dart>#!/usr/bin/env dart

library("scriptedmain");

meaningOfLife() { return 42; }

main() { print("Main: The meaning of life is ${meaningOfLife()}"); }</lang>

test.dart: <lang dart>#!/usr/bin/env dart

import("scriptedmain.dart", prefix: "scriptedmain");

main() { print("Test: The meaning of life is ${scriptedmain.meaningOfLife()}"); }</lang>

Example: <lang sh>$ ./scriptedmain.dart Main: The meaning of life is 42 $ ./test.dart Test: The meaning of life is 42</lang>

Emacs Lisp

Emacs has scripted main, though older versions require an obscure shebang syntax.

scriptedmain.el

<lang lisp>:;exec emacs -batch -l $0 -f main $*

Shebang from John Swaby http://www.emacswiki.org/emacs/EmacsScripts

(defun meaning-of-life () 42)

(defun main ()

(message "Main: The meaning of life is %d" (meaning-of-life)))</lang>

test.el

<lang lisp>:;exec emacs -batch -l $0 -f main $*

Shebang from John Swaby http://www.emacswiki.org/emacs/EmacsScripts

(defun main ()

(setq load-path (cons default-directory load-path))
(load "scriptedmain.el" nil t)
(message "Test: The meaning of life is %d" (meaning-of-life)))</lang>

Erlang

Erlang has scripted main by default. scriptedmain.erl must be compiled before test.erl can access its functions.

Makefile: <lang make>all: t

t: scriptedmain.beam test.beam erl -noshell -s scriptedmain erl -noshell -s test

scriptedmain.beam: scriptedmain.erl erlc scriptedmain.erl

test.beam: test.erl erlc test.erl

clean: -rm *.beam</lang>

scriptedmain.erl: <lang erlang>-module(scriptedmain). -export([meaning_of_life/0, start/0]).

meaning_of_life() -> 42.

start() ->

 io:format("Main: The meaning of life is ~w~n", [meaning_of_life()]),
 init:stop().</lang>

test.erl: <lang erlang>-module(test). -export([start/0]). -import(scriptedmain, [meaning_of_life/0]).

start() ->

 io:format("Test: The meaning of life is ~w~n", [meaning_of_life()]),
 init:stop().</lang>

F#

Note 1: F# supports the scriptedmain behavior, but F# does not support hybrid script-compiled code files. The following programs work provided that they are compiled and then run, as .fs files, not interpreted or dotslashed as .fsx files.

Note 2: fsharpc has a backwards file ordering: Specify any dependencies BEFORE the code that depends on them.

Note 3: fsharpc also has that unpredictable DOS-flavored command line flag syntax, so the --out requires a colon between it and its value, and -h only generates an error; use --help instead.

Note 4: In Unix, mono is required to run F# executables. In Windows, mono is not required for execution.

Example:

<lang sh>$ make fsharpc --out:scriptedmain.exe ScriptedMain.fs fsharpc --out:test.exe ScriptedMain.fs Test.fs $ mono scriptedmain.exe Main: The meaning of life is 42 $ mono test.exe Test: The meaning of life is 42</lang>

Makefile:

<lang make>all: scriptedmain.exe test.exe

scriptedmain.exe: ScriptedMain.fs fsharpc --nologo --out:scriptedmain.exe ScriptedMain.fs

test.exe: Test.fs ScriptedMain.fs fsharpc --nologo --out:test.exe ScriptedMain.fs Test.fs

clean: -rm *.exe</lang>

ScriptedMain.fs:

<lang fsharp>namespace ScriptedMain

module ScriptedMain =

   let meaningOfLife = 42

   let main =
       printfn "Main: The meaning of life is %d" meaningOfLife</lang>

Test.fs:

<lang fsharp>module Test =

   open ScriptedMain

   let main =
       printfn "Test: The meaning of life is %d" ScriptedMain.meaningOfLife</lang>

Factor

Note: The INCLUDE/INCLUDING macros must be added to the ~/.factor-rc configuration file.

Example:

<lang sh>$ ./scriptedmain.factor Main: The meaning of life is 42 $ ./test.factor Test: The meaning of life is 42</lang>

~/.factor-rc:

<lang factor>! INCLUDING macro that imports source code files in the current directory

USING: kernel vocabs.loader parser sequences lexer vocabs.parser ; IN: syntax

include-vocab ( vocab -- ) dup ".factor" append parse-file append use-vocab ;

SYNTAX: INCLUDING: ";" [ include-vocab ] each-token ;</lang>

scriptedmain.factor:

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

USING: io math.parser ; IN: scriptedmain

meaning-of-life ( -- n ) 42 ;

main ( -- ) meaning-of-life "Main: The meaning of life is " write number>string print ;

MAIN: main</lang>

test.factor:

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

INCLUDING: scriptedmain ; USING: io math.parser ; IN: test

main ( -- ) meaning-of-life "Test: The meaning of life is " write number>string print ;

MAIN: main</lang>

Forth

Given this awful running reference:

<lang forth>42 constant Douglas-Adams

go ( -- )

 ." The meaning of life is " Douglas-Adams . cr ;</lang>

The bulk of Forth systems provide a way to generate an executable that enters GO (ar any word) on start.

Works with: SwiftForth version 4.0

<lang forth>' go 'MAIN ! program douglas-adams</lang>

Which creates a file named 'douglas-adams' that you can then run. If this is all in the same file, you can load the file, test parts of it, and then exit (or shell out) to run the executable.

A unix script requires that '#!' be a comment and that the system have some #!-compatible arguments.

Works with: gforth

<lang forth>#! /usr/bin/env gforth

42 constant Douglas-Adams .( The meaning of life is ) Douglas-Adams . cr bye</lang>

Adding #! as a comment, as gforth does, is trivial. For a means by which this script could distinguish between 'scripted execution' and otherwise, a symlink like 'forthscript' could easily be used, and the zeroth OS argument tested for, but there's no convention.

Works with: gforth

<lang forth>#! /usr/bin/env forthscript

42 constant Douglas-Adams

s" forthscript" 0 arg compare 0= [IF]

 .( The meaning of life is ) Douglas-Adams . cr bye

[THEN]

cr .( Why aren't you running this as a script? It only provides a constant.)</lang>

Go

Makefile:

<lang make>include $(GOROOT)/src/Make.inc TARG=scriptname GOFILES=scriptname.go include $(GOROOT)/src/Make.cmd</lang>

scriptname.go:

<lang go>package main

import ("os"; "fmt")

func main() { program := os.Args[0] fmt.Println("Program:", program) }</lang>

Groovy

Example:

<lang sh>$ ./ScriptedMain.groovy Main: The meaning of life is 42 $ ./Test.groovy Test: The meaning of life is 42</lang>

ScriptedMain.groovy:

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

class ScriptedMain { static def meaningOfLife = 42

static main(args) { println "Main: The meaning of life is " + meaningOfLife } }</lang>

Test.groovy:

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

println "Test: The meaning of life is " + ScriptedMain.meaningOfLife</lang>

Haskell

Haskell has scripted main, but getting scripted main to work with compiled scripts is tricky.

<lang sh>$ runhaskell scriptedmain.hs Main: The meaning of life is 42 $ runhaskell test.hs Test: The meaning of life is 42 $ ghc -fforce-recomp -o scriptedmain -main-is ScriptedMain scriptedmain.hs $ ./scriptedmain Main: The meaning of life is 42 $ ghc -fforce-recomp -o test -main-is Test test.hs scriptedmain.hs $ ./test Test: The meaning of life is 42</lang>

scriptedmain.hs

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

-- Compile: -- -- ghc -fforce-recomp -o scriptedmain -main-is ScriptedMain scriptedmain.hs

module ScriptedMain where

meaningOfLife :: Int meaningOfLife = 42

main :: IO () main = putStrLn $ "Main: The meaning of life is " ++ show meaningOfLife</lang>

test.hs

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

-- Compile: -- -- ghc -fforce-recomp -o test -main-is Test test.hs scriptedmain.hs

module Test where

import ScriptedMain hiding (main)

main :: IO () main = putStrLn $ "Test: The meaning of life is " ++ show meaningOfLife</lang>

Io

ScriptedMain.io:

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

ScriptedMain := Object clone ScriptedMain meaningOfLife := 42

main := method( "Main: The meaning of life is #{ScriptedMain meaningOfLife}" interpolate println )

if (System args size > 0 and System args at(0) containsSeq("ScriptedMain"), main)</lang>

test.io:

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

main := method( "Test: The meaning of life is #{ScriptedMain meaningOfLife}" interpolate println )

if (System args size > 0 and System args at(0) containsSeq("test"), main)</lang>

<lang sh>$ ./ScriptedMain.io Main: The meaning of life is 42 $ ./test.io Test: The meaning of life is 42</lang>

J

scriptedmain.j:

<lang j>#!/usr/bin/env jconsole

load 'regex'

meaningOfLife =: 42

main =: monad : 0 echo 'Main: The meaning of life is ', > 'd' (8!:0) meaningOfLife exit )

program =: monad : 0 if. (#ARGV) > 1 do. > 1 { ARGV else. 'Interpreted' end. )

shouldrun =: monad : 0 if. '.*scriptedmain.*' rxeq program 0 do. main 0 end. )

shouldrun 0</lang>

test.j:

<lang j>#!/usr/bin/env jconsole

load 'scriptedmain.j'

echo 'Test: The meaning of life is ', > 'd' (8!:0) meaningOfLife

exit </lang>

Example:

<lang sh>$ ./scriptedmain.j Main: The meaning of life is 42 $ ./test.j Test: The meaning of life is 42</lang>

Java

Java has scripted main by default.

ScriptedMain.java

<lang java>public class ScriptedMain { public static int meaningOfLife() { return 42; }

public static void main(String[] args) { System.out.println("Main: The meaning of life is " + meaningOfLife()); } }</lang>

Test.java

<lang java>public class Test { public static void main(String[] args) { System.out.println("Test: The meaning of life is " + ScriptedMain.meaningOfLife()); } }</lang>

LLVM

LLVM can have scripted main a la C, using the weak attribute.

<lang sh>$ make llvm-as scriptedmain.ll llc scriptedmain.bc gcc -o scriptedmain scriptedmain.s ./scriptedmain Main: The meaning of life is 42 llvm-as test.ll llc test.bc gcc -o test test.s scriptedmain.s ./test Test: The meaning of life is 42</lang>

Makefile

<lang make>EXECUTABLE_SM=scriptedmain EXECUTABLE_TEST=test

all: test.ll scriptedmain.s llvm-as test.ll llc test.bc gcc -o $(EXECUTABLE_TEST) test.s scriptedmain.s ./$(EXECUTABLE_TEST)

scriptedmain.s: scriptedmain.ll llvm-as scriptedmain.ll llc scriptedmain.bc gcc -o $(EXECUTABLE_SM) scriptedmain.s ./$(EXECUTABLE_SM)

clean: -rm $(EXECUTABLE_TEST) -rm $(EXECUTABLE_SM) -rm test.s -rm test.bc -rm scriptedmain.s -rm scriptedmain.bc</lang>

scriptedmain.ll

<lang llvm>@msg_main = internal constant [33 x i8] c"Main: The meaning of life is %d\0A\00"

declare i32 @printf(i8* noalias nocapture, ...)

define i32 @meaning_of_life() { ret i32 42 }

define weak i32 @main(i32 %argc, i8** %argv) { %meaning = call i32 @meaning_of_life()

call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([33 x i8]* @msg_main, i32 0, i32 0), i32 %meaning)

ret i32 0 }</lang>

test.ll

<lang llvm>@msg_test = internal constant [33 x i8] c"Test: The meaning of life is %d\0A\00"

declare i32 @printf(i8* noalias nocapture, ...)

declare i32 @meaning_of_life()

define i32 @main(i32 %argc, i8** %argv) { %meaning = call i32 @meaning_of_life()

call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([33 x i8]* @msg_test, i32 0, i32 0), i32 %meaning)

ret i32 0 }</lang>

Lua

Lua has scripted main by default because files are largely indistinguishable from functions semantically (they compile to Lua functions.) Ellipses is Lua's var-arg syntax for functions, and, therefore, for files as well.

scriptedmain.lua

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

function meaningoflife() return 42 end

function main(arg) print("Main: The meaning of life is " .. meaningoflife()) end

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

test.lua

<lang lua>#!/usr/bin/env lua sm = require("scriptedmain") print("Test: The meaning of life is " .. sm.meaningoflife())</lang>

Mathematica

scriptedmain.ma <lang mathematica>#!/usr/bin/env MathKernel -script

MeaningOfLife[] = 42

ScriptName[] = Piecewise[ { {"Interpreted", Position[$CommandLine, "-script", 1] == {}} }, $CommandLine[[Position[$CommandLine, "-script", 1]1,1 + 1]] ]

Program = ScriptName[];

If[StringMatchQ[Program, ".*scriptedmain.*"], Print["Main: The meaning of life is " <> ToString[MeaningOfLife[]]] ]</lang>

test.ma: <lang mathematica>#!/usr/bin/env MathKernel -script

Get["scriptedmain.ma"]

Print["Test: The meaning of life is " <> ToString[MeaningOfLife[]]]</lang>

Example: <lang sh>$ ./scriptedmain.ma Main: The meaning of life is 42 $ ./test.ma Test: The meaning of life is 42</lang>

In Mac and Windows, the output will be surrounded by spurious quotes.

Mozart/Oz

Makefile: <lang make>all: run

run: scriptedmain test ./scriptedmain ./test

scriptedmain: scriptedmain.oz ozc -x scriptedmain.oz

scriptedmain.ozf: scriptedmain.oz ozc -c scriptedmain.oz

test: scriptedmain.ozf test.oz ozc -x test.oz

clean: -rm test -rm scriptedmain -rm *.ozf -rm *.exe </lang>

scriptedmain.oz: <lang oz>functor export

 meaningOfLife: MeaningOfLife

import

 System
 Application
 Property
 Regex at 'x-oz://contrib/regex'

define

 fun {MeaningOfLife} 42 end

 local ScriptName = {Property.get 'application.url'} in
   if {Regex.search "scriptedmain" ScriptName} \= false then
     {System.printInfo "Main: The meaning of life is "#{Int.toString {MeaningOfLife}}#"\n"}
     {Application.exit 0}
   end
 end

end </lang>

test.oz: <lang oz>functor import

 ScriptedMain
 System
 Application
 Property
 Regex at 'x-oz://contrib/regex'

define

 local ScriptName = {Property.get 'application.url'} in
   if {Regex.search "test" ScriptName} \= false then
     {System.printInfo "Test: The meaning of life is "#{Int.toString {ScriptedMain.meaningOfLife}}#"\n"}
     {Application.exit 0}
   end
 end

end</lang>

newLISP

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

scriptedmain.lsp

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

(context 'SM)

(define (SM:meaning-of-life) 42)

(define (main) (println (format "Main: The meaning of life is %d" (meaning-of-life))) (exit))

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

(context MAIN)</lang>

test.lsp

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

(load "scriptedmain.lsp") (println (format "Test: The meaning of life is %d" (SM:meaning-of-life))) (exit)</lang>

Node.js

Node.js has scripted main.

scriptedmain.js

<lang javascript>#!/usr/bin/env node

function meaningOfLife() { return 42; }

exports.meaningOfLife = meaningOfLife;

function main() { console.log("Main: The meaning of life is " + meaningOfLife()); }

if (!module.parent) { main(); }</lang>

test.js

<lang javascript>#!/usr/bin/env node

var sm = require("./scriptedmain");

console.log("Test: The meaning of life is " + sm.meaningOfLife());</lang>

Objective-C

scriptedmain.h:

<lang objc>#import <objc/Object.h>

@interface ScriptedMain: Object {}

+ (int)meaningOfLife;

@end</lang>

scriptedmain.m:

<lang objc>#import "scriptedmain.h"

import <Foundation/Foundation.h>

@implementation ScriptedMain

+ (int)meaningOfLife { return 42; }

@end

int __attribute__((weak)) main(int argc, char **argv) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

printf("Main: The meaning of life is %d\n", [ScriptedMain meaningOfLife]);

[pool drain];

return 0; }</lang>

test.m:

<lang objc>#import "scriptedmain.h"

import <Foundation/Foundation.h>

int main(int argc, char **argv) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];

printf("Test: The meaning of life is %d\n", [ScriptedMain meaningOfLife]);

[pool drain];

return 0; }</lang>

<lang sh>$ gcc -o scriptedmain -lobjc -framework foundation scriptedmain.m $ gcc -o test -lobjc -framework foundation test.m scriptedmain.m $ ./scriptedmain Main: The meaning of life is 42 $ ./test Test: The meaning of life is 42</lang>

OCaml

scriptedmain.ml

<lang ocaml>if true then ignore begin let kkkk _ _ _ _ _ = 0 in kkkk "exec" "ocaml" "str.cma" "$0" "$@" + let fi = 0 and exit _ _ = 0 in if false then exit fi true else 0 end;;

(*

Interpret:

./scriptedmain.ml

Compile:

ocamlc -o scriptedmain -linkall str.cma scriptedmain.ml

Run:

./scriptedmain

)

let meaning_of_life : int = 42

let main () = print_endline ("Main: The meaning of life is " ^ string_of_int meaning_of_life)

let _ = let program = Sys.argv.(0) and re = Str.regexp "scriptedmain" in try let _ = Str.search_forward re program 0 in main () with Not_found -> ()</lang>

test.ml

<lang ocaml>if true then ignore begin let kkkk _ _ _ _ _ _ = 0 in kkkk "exec" "ocaml" "str.cma" "scriptedmain.cmo" "$0" "$@" + let fi = 0 and exit _ _ = 0 in if false then exit fi true else 0 end;;

(*

Compile:

ocamlc -o test -linkall str.cma scriptedmain.ml test.ml

Interpret:

./test.ml

Run:

./test

)

let main () = print_endline ("Test: The meaning of life is " ^ string_of_int Scriptedmain.meaning_of_life)

let _ = let program = Sys.argv.(0) and re = Str.regexp "test" in try let _ = Str.search_forward re program 0 in main () with Not_found -> ()</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.

meaningoflife.m

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

function y = meaningoflife() y = 42; endfunction

function main() printf("Main: The meaning of life is %d", meaningoflife()); endfunction

main();</lang>

test.m

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

printf("Test: The meaning of life is %d", meaningoflife());</lang>

Pascal

Works with: Free_Pascal

Makefile:

<lang make>all: scriptedmain

scriptedmain: scriptedmain.pas fpc -dscriptedmain scriptedmain.pas

test: test.pas scriptedmain fpc test.pas

clean: -rm test -rm scriptedmain -rm *.o -rm *.ppu</lang>

scriptedmain.pas:

<lang pascal>{$IFDEF scriptedmain} program ScriptedMain; {$ELSE} unit ScriptedMain; interface function MeaningOfLife () : integer; implementation {$ENDIF} function MeaningOfLife () : integer; begin MeaningOfLife := 42 end; {$IFDEF scriptedmain} begin write('Main: The meaning of life is: '); writeln(MeaningOfLife()) {$ENDIF} end.</lang>

test.pas:

<lang pascal>program Test; uses ScriptedMain; begin write('Test: The meaning of life is: '); writeln(MeaningOfLife()) end.</lang>

Example:

<lang sh>$ make $ ./scriptedmain Main: The meaning of life is: 42 $ make test $ ./test Test: The meaning of life is: 42</lang>

Perl

Perl has scripted main. The code inside unless(caller) { ... } only runs when Life.pm is the main program.

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

Life.pm

package Life;

use strict; use warnings;

sub meaning_of_life { return 42; }

unless(caller) { print "Main: The meaning of life is " . meaning_of_life() . "\n"; }</lang>

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

death.pl

use strict; use warnings;

use Life;

print "Life means " . Life::meaning_of_life . ".\n"; print "Death means invisible scary skeletons.\n";</lang>

Perl 6

Perl 6 automatically calls MAIN on direct invocation, but this may be a multi dispatch, so a library may have multiple "scripted mains". <lang perl6>class LUE {

   has $.answer = 42;

}

multi MAIN ('test') {

   say "ok" if LUE.new.answer == 42;

}

multi MAIN ('methods') {

   say ~LUE.^methods;

}</lang>

PHP

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

scriptedmain.php

<lang php><?php function meaning_of_life() { return 42; }

function main($args) { echo "Main: The meaning of life is " . meaning_of_life() . "\n"; }

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

test.php

PicoLisp

PicoLisp normally does it the other way round: It calls main from the command line with the '-' syntax if desired. Create an executable file (chmod +x) "life.l": <lang PicoLisp>#!/usr/bin/picolisp /usr/lib/picolisp/lib.l

(de meaningOfLife ()

  42 )

(de lifemain ()

  (prinl "Main: The meaning of life is " (meaningOfLife))
  (bye) )</lang>

and an executable file (chmod +x) "test.l": <lang PicoLisp>#!/usr/bin/picolisp /usr/lib/picolisp/lib.l

(load "life.l")

(prinl "Test: The meaning of life is " (meaningOfLife)) (bye)</lang> Test:

$ ./life.l -lifemain
Main: The meaning of life is 42

$ ./test.l
Test: The meaning of life is 42

Python

Python has scripted main.

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

life.py

def meaning_of_life():

 return 42

if __name__ == "__main__":

 print("Main: The meaning of life is %s" % meaning_of_life())</lang>

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

death.py

from life import meaning_of_life

print("Life means %s." % meaning_of_life()) print("Death means invisible scary skeletons.")</lang>

R

A way to check if code is running at "top level" is to check length(sys.frames()). This value will be zero for a file being run with Rscript, the --file= argument, or at the command line, and will be greater than 0 in all other conditions (such as package loading or code being sourced from another file.)

<lang R>#!/usr/bin/env Rscript

meaningOfLife <- function() { 42 }

main <- function(args) { cat("Main: The meaning of life is", meaningOfLife(), "\n") }

if (length(sys.frames()) > 0) {

       args <- commandArgs(trailingOnly = FALSE)

main(args) q("no") }</lang>

test.R

<lang R>#!/usr/bin/env Rscript

source("scriptedmain.R")

cat("Test: The meaning of life is", meaningOfLife(), "\n")

q("no")</lang>

Racket

scriptedmain.rkt: <lang racket>#!/usr/bin/env racket

lang racket

(provide meaning-of-life)

(define (meaning-of-life) 42)

(module+ main (printf "Main: The meaning of life is ~a\n" (meaning-of-life)))</lang>

test.rkt: <lang racket>#!/usr/bin/env racket

lang racket

(module+ main (require "scriptedmain.rkt") (printf "Test: The meaning of life is ~a\n" (meaning-of-life)))</lang>

REXX

<lang rexx>/*REXX program to detect whether or not it is a "scripted main" program.*/

parse upper source . howInvoke . if howInvoke \== 'COMMAND' then do

                               /* maybe say something here? */
                               return 
                               end
         /* ┌────────────────────────────────────────────────┐
            │  At this point, we know that this program was  │
            │  invoked via the "command line" and not via    │
            │  another program.                              │
            └────────────────────────────────────────────────┘  */

say 'and away we go ...'</lang> Note: Actually another program can invoke the above (ma.rex) as a command: <lang>'rexx ma'</lang>

Ruby

Ruby has scripted main.

<lang ruby># life.rb

def meaning_of_life

end

if __FILE__ == $0

 puts "Main: The meaning of life is #{meaning_of_life}"

end</lang>

<lang ruby># death.rb

require 'life'

puts "Life means #{meaning_of_life}." puts "Death means invisible scary skeletons."</lang>

Rust

Makefile: <lang make>all: scriptedmain

scriptedmain: scriptedmain.rs rustc scriptedmain.rs

test: test.rs scriptedmain.rs rustc --lib scriptedmain.rs rustc test.rs -L .

clean: -rm test -rm -rf *.dylib -rm scriptedmain -rm -rf *.dSYM</lang>

scriptedmain.rs: <lang rust>#[link(name = "scriptedmain")];

use std;

fn meaning_of_life() -> int { ret 42; }

fn main() { std::io::println("Main: The meaning of life is " + core::int::to_str(meaning_of_life(), 10u)); }</lang>

test.rs: <lang rust>use scriptedmain; use std;

fn main() { std::io::println("Test: The meaning of life is " + core::int::to_str(scriptedmain::meaning_of_life(), 10u)); }</lang>

Example: <lang sh>$ make $ make test $ ./scriptedmain Main: The meaning of life is 42 $ ./test Test: The meaning of life is 42</lang>

SAC

Makefile: <lang make>all: scriptedmain

scriptedmain: ScriptedMain.sac sac2c -o scriptedmain ScriptedMain.sac -Dscriptedmain

test: test.sac ScriptedMain.sac sac2c ScriptedMain.sac sac2c -o test test.sac

clean: -rm test -rm test.c -rm libScriptedMainTree.so -rm libScriptedMainMod.so -rm libScriptedMainMod.a -rm scriptedmain -rm scriptedmain.c</lang>

ScriptedMain.sac: <lang c>#ifndef scriptedmain module ScriptedMain;

endif

use StdIO: all; use Array: all; export all;

int meaning_of_life() { return(42); }

ifdef scriptedmain

int main() { printf("Main: The meaning of life is %d\n", meaning_of_life()); return(0); }

endif</lang>

test.sac: <lang c>use StdIO: all; use Array: all; use ScriptedMain: all;

int main() { printf("Test: The meaning of life is %d\n", meaning_of_life()); return(0); }</lang>

Example: <lang sh>$ make $ make test $ ./scriptedmain Main: The meaning of life is 42 $ ./test Test: The meaning of life is 42</lang>

Scala

Library: Scala

Unix shell script

This code must be stored as a shell script. <lang bash>#!/bin/sh exec scala "$0" "$@" !#

 def hailstone(n: Int): Stream[Int] =
      n #:: (if (n == 1) Stream.empty else hailstone(if (n % 2 == 0) n / 2 else n * 3 + 1))

 val nr = argv.headOption.map(_.toInt).getOrElse(27)
 val collatz = hailstone(nr)
 println(s"Use the routine to show that the hailstone sequence for the number: $nr.")
 println(collatz.toList)
 println(s"It has ${collatz.length} elements.")</lang>

Windows Command Scrip

This code must be stored as a Windows Command Script e.g. Hailstone.cmd <lang winbatch>::#! @echo off call scala %0 %* pause goto :eof

!#

 def hailstone(n: Int): Stream[Int] =
      n #:: (if (n == 1) Stream.empty else hailstone(if (n % 2 == 0) n / 2 else n * 3 + 1))

 val nr = argv.headOption.map(_.toInt).getOrElse(27)
 val collatz = hailstone(nr)
 println(s"Use the routine to show that the hailstone sequence for the number: $nr.")
 println(collatz.toList)
 println(s"It has ${collatz.length} elements.")

</lang>

Output:

C:\>Hailstone.cmd 42

Use the routine to show that the hailstone sequence for the number: 42. List(42, 21, 64, 32, 16, 8, 4, 2, 1)

It has 9 elements.

Smalltalk

Note that the ScriptedMain package must be installed in order for test.st to access code from scriptedmain.st.

Example

<lang shell>$ gst-package -t ~/.st package.xml &>/dev/null

$ ./scriptedmain.st Main: The meaning of life is 42

$ ./test.st Test: The meaning of life is 42</lang>

package.xml

<lang xml><packages> <package> <name>ScriptedMain</name> <filein>scriptedmain.st</filein> <file>scriptedmain.st</file> </package> </packages></lang>

scriptedmain.st

<lang smalltalk>"exec" "gst" "-f" "$0" "$0" "$@" "exit"

Object subclass: ScriptedMain [ ScriptedMain class >> meaningOfLife [ ^42 ] ]

| main |

main := [ Transcript show: 'Main: The meaning of life is ', ((ScriptedMain meaningOfLife) printString); cr. ].

(((Smalltalk getArgc) > 0) and: [ ((Smalltalk getArgv: 1) endsWith: 'scriptedmain.st') ]) ifTrue: [ main value. ].</lang>

test.st

<lang smalltalk>"exec" "gst" "-f" "$0" "$0" "$@" "exit"

" PackageLoader fileInPackage: 'ScriptedMain'.

Transcript show: 'Test: The meaning of life is ', ((ScriptedMain meaningOfLife) printString); cr.</lang>

Tcl

<lang tcl>proc main {args} {

   puts "Directory: [pwd]"
   puts "Program: $::argv0"
   puts "Number of args: [llength $args]"
   foreach arg $args {puts "Arg: $arg"}

}

if {$::argv0 eq [info script]} {

   main {*}$::argv

}</lang>

UNIX Shell

Bash has scripted main.

scriptedmain.sh

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

meaning_of_life() { return 42 }

main() { meaning_of_life echo "Main: The meaning of life is $?" }

if "$BASH_SOURCE" == "$0" then

   main

fi</lang>

test.sh

<lang sh>#!/usr/bin/env sh source scriptedmain.sh meaning_of_life echo "Test: The meaning of life is $?"</lang>

ZX Spectrum Basic

On the ZX Spectrum, there is no main function as such, however a saved program can be made to start running from a particular line number by providing the line number as a parameter to save command. If the program is being merged as a module, then it does not run automatically. The following example will save the program in memory so that it starts running from line 500:

<lang zxbasic>SAVE "MYPROG" LINE 500: REM For a program with main code starting at line 500</lang>