Program name

Program name is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

It is useful to programmatically access a program's name, e.g. for determining whether the user ran "python hello.py", or "python hellocaller.py", a program importing the code from "hello.py".

Sometimes a MultilineShebang is necessary in order to provide the script name to a language's internal ARGV.

Examples from GitHub.

C

It might not be very useful for a C program to access source filenames, because C code must be compiled into an executable, and anything could have happened to the source file after the compilation. However, C can access the executable's name in argv[0].

• argv[0] might be the name of an executable in the PATH, or it might be an absolute or relative path to the executable. At least with Unix, the parent process can set argv[0] to any string, so argv[0] might not be the real name. It is best to pretend that argv[0] has the correct value, but mind that argv[0] might not be an actual file.

<lang c>#include <stdio.h>

int main(int argc, char **argv) { printf("Executable: %s\n", argv[0]);

return 0; }</lang>

To get the source information about some part of code, use compiler defined macros. Most compilers support them or some variation of. <lang c>#include <stdio.h>

int main() { printf("This code was in file %s in function %s, at line %d\n",\ __FILE__, __FUNCTION__, __LINE__); return 0; }</lang>

BSD

BSD provides two more ways to get the program's name.

1. __progname is the filename from argv[0] (so if argv[0] is a path, then __progname is only the filename). No header file declares __progname, so programs must declare extern char __progname; to use it.
2. p_comm always gives the real filename of the executable, even if argv[0] has a different name. p_comm is a field in the process information. Tools like ps(1) and top(1) use p_comm, but almost no other program uses p_comm, because the API is so difficult.

Build the next program with make myname LDLIBS=-lkvm

Library: BSD libc

Works with: OpenBSD version 4.9

<lang c>/* myname.c */

1. include <sys/param.h>
2. include <sys/sysctl.h> /* struct kinfo_proc2 */
3. include <err.h>
4. include <fcntl.h> /* O_RDONLY */
5. include <kvm.h>
6. include <limits.h> /* _POSIX2_LINE_MAX */
7. include <stdio.h>

int main(int argc, char **argv) { extern char *__progname; /* from crt0.o */

struct kinfo_proc2 *procs; kvm_t *kd; int cnt; char errbuf[_POSIX2_LINE_MAX];

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

kd = kvm_openfiles(NULL, NULL, NULL, KVM_NO_FILES, errbuf); if (kd == NULL) errx(1, "%s", errbuf); procs = kvm_getproc2(kd, KERN_PROC_PID, getpid(), sizeof procs[0], &cnt); if (procs == NULL) errx(1, "%s", kvm_geterr(kd));

printf("p_comm: %s\n", procs[0].p_comm);

kvm_close(kd); return 0; }</lang>

The program can have three different names!

$ perl -e 'exec {"./myname"} "/nobin/fakename"' 
argv[0]: /nobin/fakename
__progname: fakename
p_comm: myname

C++

C++ has difficulty accessing source code filenames, because C code must be compiled into an executable. However, C++ can access the executable's filename.

<lang cpp>#include <iostream>

using namespace std;

int main(int argc, char **argv) { char *program = argv[0]; cout << "Program: " << program << endl;

return 0; }</lang>

Chicken Scheme

Getting the program name is tricky. When interpreted, the script name will be printed. When compiled, the executable name will be printed.

<lang scheme>#!/bin/bash

1. |

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

(use posix) (require-extension srfi-1) ; lists (require-extension srfi-13) ; strings

(define (main args) (let ((prog (cdr (program)))) (display (format "Program: ~a\n" prog)) (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>

Clojure

If the shebang is used to run the script directly, this prints the script name. Otherwise, it prints nil.

<lang clojure>":";exec clj -m `basename $0 .clj` $0 ${1+"$@"} ":";exit

(ns scriptname (:gen-class))

(defn -main [& args] (def program (nth args 0)) (println "Program:" program))</lang>

Common Lisp

Shebangs require a special tweak to ~/.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>

<lang lisp>#!/bin/bash

1. |

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

Usage

./scriptname.lisp

(defun main (args)

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

D

Will print name of executable. <lang d>import std.stdio;

void main(string[] args) {

   writeln(args[0]);	

}</lang>

Emacs Lisp

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

Shebang from John Swaby

http://www.emacswiki.org/emacs/EmacsScripts

(defun main ()

(let ((program (nth 2 command-line-args)))
 (message "Program: %s" program)))</lang>

Erlang

Erlang's macros hold information about the running module.

<lang erlang>-module(scriptname).

main(_) -> Program = ?FILE, io:format("Program: ~s~n", [Program]).</lang>

Go

Prints the executable's filename. <lang go>package main

import ("os"; "fmt")

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

Haskell

Haskell has an impure function for this.

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

module ScriptName where

import System (getProgName)

main :: IO () main = do program <- getProgName putStrLn $ "Program: " ++ program</lang>

Java

On one hand, this task is trivial for Java. Java code is (usually) compiled into bytecode as class files. There is exactly one class file per class, named <class name>.class (regardless of what the original source files were called or how classes were organized in the source). One executes Java code by executing some class which contains a main method, by running the command java <class name> <possible arguments>. Hence, it is guaranteed that the "name" of the executable is the class name (possibly prepended by package names, using the usual Java dot notation); and this is known in the main method at the time the code is written because it is the very class that the main method is in. Hence, the complicated solutions listed in this section do not gain anything that is not already known by the programmer at the time the code is written.

However, it is tedious to hard-code the class names if you need to do this in a lot of Java programs. Thus, a more interesting task is to write a snippet of Java code which, without modification, can be copy-and-pasted into the main method of any class and retrieve the class name. This is not trivial because in Java there is no way to use this in a static method to get the class it's in. Listed below are several notable, commonly-cited solutions for this.

You can get the listing of the arguments to the java command through a system property. The first one is the name of the main class that was run. This depends on a system property named "sun.java.command", which might not exist on all Java virtual machines. <lang java>// Thanks to Mwn3d public class ScriptName { public static void main(String[] args) { String program = System.getProperty("sun.java.command").split(" ")[0]; System.out.println("Program: " + program); } }</lang>

An alternate solution is to create a dummy inner class, and then retrieve its enclosing class (which is the class the main method is in) through reflection: <lang java>public class ScriptName { public static void main(String[] args) { Class c = new Object(){}.getClass().getEnclosingClass(); System.out.println("Program: " + c.getName()); } }</lang>

A solution using the security manager: <lang java>public class ScriptName { public static void main(String[] args) { Class c = System.getSecurityManager().getClassContext()[0]; System.out.println("Program: " + c.getName()); } }</lang>

A solution using the stack trace (requires Java 1.5+): <lang java>public class ScriptName { public static void main(String[] args) { String program = Thread.currentThread().getStackTrace()[1].getClassName(); System.out.println("Program: " + program); } }</lang>

LLVM

Like C, LLVM can use argv to access the executable's filename.

<lang sh>$ make llvm-as scriptname.ll llc scriptname.bc gcc -o scriptname scriptname.s ./scriptname Program: ./scriptname</lang>

Makefile

<lang make>all: scriptname.ll llvm-as scriptname.ll llc scriptname.bc gcc -o scriptname scriptname.s ./scriptname

clean: -rm scriptname -rm scriptname.s -rm scriptname.bc</lang>

<lang llvm>@msg_main = internal constant [13 x i8] c"Program: %s\0A\00"

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

define i32 @main(i32 %argc, i8** %argv) { %program = load i8** %argv call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([13 x i8]* @msg_main, i32 0, i32 0), i8* %program)

ret i32 0 }</lang>

Lua

Lua's arg is like C's argv.

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

function main(arg) local program = arg[0] print("Program: " .. program) end

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

MATLAB/Octave

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

function main() program = program_name(); printf("Program: %s", program); endfunction

main();</lang>

newLISP

newLISP has a function, (main-args int) for this.

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

(let ((program (main-args 1)))

 (println (format "Program: %s" program))
 (exit))</lang>

Node.js

Node.js has a global variable for this.

<lang javascript>#!/usr/bin/env node /*jslint nodejs:true */

function main() { var program = __filename; console.log("Program: " + program); }

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

OCaml

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

let () = let program = Sys.argv.(0) in Printf.printf "Program: %s\n" program</lang>

Perl

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

use strict; use warnings;

sub main { my $program = $0; print "Program: $program\n"; }

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

Perl 6

In Perl 6, the name of the program being executed is in the special global variable $*PROGRAM_NAME. <lang perl6>say $*PROGRAM_NAME;</lang>

PHP

PHP has a global dictionary for this.

<lang php><?php $program = $_SERVER["SCRIPT_NAME"]; echo "Program: $program\n"; ?></lang>

Python

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

import sys

def main(): program = sys.argv[0] print "Program: %s" % program

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

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

import inspect

def main(): program = inspect.getfile(inspect.currentframe()) print "Program: %s" % program

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

R

R's syntax is complicated, but doable.

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

getProgram <- function(args) { sub("--file=", "", args[grep("--file=", args)]) }

args <- commandArgs(trailingOnly = FALSE) program <- getProgram(args)

cat("Program: ", program, "\n")

q("no")</lang>

Ruby

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

def main program = __FILE__ puts "Program: #{program}" end

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

Smalltalk

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

| program |

program := Smalltalk arguments at: 1.

Transcript show: 'Program: ', program; cr.</lang>

Standard ML

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

let val program = CommandLine.name () in print ("Program: " ^ program ^ "\n") end;</lang>

Tcl

<lang tcl>#!/usr/bin/env tclsh

proc main {args} {

   set program $::argv0
   puts "Program: $program"

}

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

   main {*}$::argv

}</lang>

UNIX Shell

In Bash: <lang sh>#!/usr/bin/env sh

export program=$BASH_SOURCE echo "Program: $program"</lang>