Modulinos

It is useful to be able to run 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>

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>