Program name
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".
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 filename.
<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>
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>
Erlang
Erlang's macros hold information about the running module.
<lang erlang>-module(scriptname).
main(_) -> Program = ?FILE, io:format("Program: ~s~n", [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
Java mainly has notions of classes.
<lang java>public class ScriptName { public static void main(String[] args) { String program = new ScriptName().getClass().getName(); System.out.println("Program: " + program); } }</lang>
Node.hs
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>
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>