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By convention ARGV[0] contains the name of the script being utilized. However, this behaviour is not reliable and it is not consistent across systems. Some systems may report the name of the awk interpreter, rather than the name of the script and pathname components may be included. |
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<lang awk>BEGIN { print "The invocation name is:" ARGV[0] }</lang> |
<lang awk>BEGIN { print "The invocation name is:" ARGV[0] }</lang> |
Revision as of 17:42, 22 August 2011
![Task](http://static.miraheze.org/rosettacodewiki/thumb/b/ba/Rcode-button-task-crushed.png/64px-Rcode-button-task-crushed.png)
You are encouraged to solve this task according to the task description, using any language you may know.
The task is to programmatically obtain the name used to invoke the program. (For example determine whether the user ran "python hello.py", or "python hellocaller.py", a program importing the code from "hello.py".)
Sometimes a multiline shebang is necessary in order to provide the script name to a language's internal ARGV.
Examples from GitHub.
AWK
By convention ARGV[0] contains the name of the script being utilized. However, this behaviour is not reliable and it is not consistent across systems. Some systems may report the name of the awk interpreter, rather than the name of the script and pathname components may be included.
<lang awk>BEGIN { print "The invocation name is:" ARGV[0] }</lang>
BASIC
Many BASICs -- notably older DOS BASICs, and especially DOS MS BASICs -- do not provide any way to retrieve the program's name.
FreeBASIC
Unlike most MS BASICs, FreeBASIC provides a parsed version of COMMAND$
(called as COMMAND$(n)
). COMMAND$(0)
is the program's name:
<lang qbasic>appname = COMMAND$(0)</lang>
Additionally, FreeBASIC also provides an analog of C's argc/argv[]
, called __FB_ARGC__
and __FB_ARGV__
. __FB_ARGV__ can be used to get the program's name like this:
<lang qbasic>appname = *__FB_ARGV__(0)</lang>
See also #PowerBASIC, #Visual Basic.
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 setargv[0]
to any string, soargv[0]
might not be the real name. It is best to pretend thatargv[0]
has the correct value, but mind thatargv[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.
__progname
is the filename fromargv[0]
(so ifargv[0]
is a path, then__progname
is only the filename). No header file declares__progname
, so programs must declareextern char __progname;
to use it.p_comm
always gives the real filename of the executable, even ifargv[0]
has a different name.p_comm
is a field in the process information. Tools like ps(1) and top(1) usep_comm
, but almost no other program usesp_comm
, because the API is so difficult.
Build the next program with make myname LDLIBS=-lkvm
<lang c>/* myname.c */
- include <sys/param.h>
- include <sys/sysctl.h> /* struct kinfo_proc2 */
- include <err.h>
- include <fcntl.h> /* O_RDONLY */
- include <kvm.h>
- include <limits.h> /* _POSIX2_LINE_MAX */
- 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)); if (cnt != 1) errx(1, "impossible");
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>
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
- |
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>
Factor
<lang factor>#! /usr/bin/env factor
USING: namespaces io command-line ; IN: scriptname
- main ( -- ) script get print ;
MAIN: main</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>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>
JavaScript
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>
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>
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>
OCaml
<lang ocaml>#!/usr/bin/env ocaml
let () = let program = Sys.argv.(0) in Printf.printf "Program: %s\n" program</lang>
Octave
<lang octave>#!/usr/bin/env octave -qf
function main() program = program_name(); printf("Program: %s", program); endfunction
main();</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: $program\n"; ?></lang>
PicoLisp
The function 'cmd' returns the command name. <lang PicoLisp>: (cmd) -> "/usr/bin/picolisp"</lang>
PowerBASIC
Previous versions of PowerBASIC (PB/Win 8 or older; PB/CC 4 or older) have to make an API call:
<lang powerbasic>#INCLUDE "Win32API.inc" '[...] DIM fullpath AS ASCIIZ * 260, appname AS STRING GetModulefullpathA 0, fullpath, 260 IF INSTR(fullpath, "\") THEN
appname = MID$(fullpath, INSTR(-1, fullpath, "\") + 1)
ELSE
appname = fullpath
END IF</lang>
Recent versions of PowerBASIC provide the EXE
object; EXE.NAME$
returns the program's name, while EXE.NAMEX$
returns the program's name and extension. (EXE.EXTN$
returns the extension only.) So, to get the program's name, we do this:
<lang powerbasic>appname = EXE.NAMEX$</lang>
Python
Python has at least two ways to get the script name: the traditional ARGV and the inspect module.
<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>
REXX
REXX does not support the use of arg(0) to access the program name. A workaround is to use a shell wrapper script to obtain and provide the invocation name of the wrapper:
<lang sh>#!/bin/sh rexxbit.rexx $0 $*</lang>
Here is a rexx script that makes use of this:
<lang rexx>say "The program is called " arg(1)</lang>
Ruby
<lang ruby>#!/usr/bin/env ruby
puts "Path: #{$0}" puts "Name: #{File.basename $0}"</lang>
For example,
$ ruby script.rb Path: script.rb Name: script.rb $ ruby ../rc/script.rb Path: ../rc/script.rb Name: script.rb $ ruby -e 'load "script.rb"' Path: -e Name: -e
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
- |
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>
Smalltalk
Note that this only works when run as "./scriptname.st", because the shebang must force the script name onto ARGV.
<lang smalltalk>"exec" "gst" "-f" "$0" "$0" "$@" "exit"
| program |
program := Smalltalk getArgv: 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
<lang bash>#!/bin/sh
echo "Program: $0"</lang>
Visual Basic
Visual Basic provides the App
object, which has a property called EXEName
that contains the program's filename without the extension. (For most uses, this doesn't matter, but for code shared between, for example, a program and a screensaver, it can be important.) So, if a program is called "MyVBapp.exe", retreiving the value of App.EXEName
would look like this:
<lang vb>appname = App.EXEName 'appname = "MyVBapp"</lang>
Alternately, Visual Basic can make an API call: <lang vb>Declare Function GetModuleFileName Lib "kernel32" Alias "GetModuleFileNameA" (ByVal hModule As Long, ByVal lpFileName As String, ByVal nSize As Long) As Long Dim fullpath As String * 260, appname As String, namelen As Long namelen = GetModuleFileName (0, fullpath, 260) fullpath = Left$(fullpath, namelen) If InStr(fullpath, "\") Then
appname = Mid$(fullpath, InStrRev(fullpath, "\") + 1)
Else
appname = fullpath
End If</lang>
- Programming Tasks
- Basic language learning
- AWK
- BASIC
- C
- BSD libc
- C++
- Clojure
- Common Lisp
- D
- Emacs Lisp
- Erlang
- Factor
- Go
- Haskell
- Java
- JavaScript
- LLVM
- Lua
- NewLISP
- OCaml
- Octave
- Octave examples needing attention
- Examples needing attention
- Perl
- Perl 6
- PHP
- PicoLisp
- PowerBASIC
- Python
- R
- REXX
- Ruby
- Scheme
- Smalltalk
- Standard ML
- Tcl
- UNIX Shell
- Visual Basic
- ZX Spectrum Basic/Omit
- Initialization