Command-line argument parsing

Different Command-line argument parsing methods are used by different programming languages to parse command-line arguments.

Programming languages

C

Main article: C_syntax § Command-line_arguments

C uses argv to process command-line arguments.

Java

An example of Java argument parsing would be:

public class Echo {
    public static void main (String[] args) {
        for (String s: args) {
            System.out.println(s);
        }
    }
}

Perl

Perl uses $ARGV.

PHP

PHP uses argc as a count of arguments and argv as an array containing the values of the arguments. To create an array from command-line arguments in the -foo:bar format, the following might be used:

$args = parseArgs( $argv );
echo getArg( $args, 'foo' );

function parseArgs( $args ) {
	foreach( $args as $arg ) {
		$tmp = explode( ':', $arg, 2 );
		if( $arg[0] == "-" ) {
			$args[ substr( $tmp[0], 1 ) ] = $tmp[1];
		}
	}
	return $args;
}

function getArg( $args, $arg ) {
	if( isset( $args[$arg] ) ) {
		return $args[$arg];
	}
	return false;
}

PHP can also use getopt().

Python

Python uses sys.argv, e.g.:

import sys
for arg in sys.argv:
  print arg

Python also has a module called argparse in the standard library for parsing command-line arguments.

Racket

Racket uses a current-command-line-arguments parameter, and provides a racket/cmdline library for parsing these arguments. Example:

#lang racket

(require racket/cmdline)

(define smile? (make-parameter #t))
(define nose?  (make-parameter #false))
(define eyes   (make-parameter ":"))

(command-line #:program "emoticon"

              #:once-any ; the following two are mutually exclusive
              [("-s" "--smile") "smile mode" (smile? #true)]
              [("-f" "--frown") "frown mode" (smile? #false)]

              #:once-each
              [("-n" "--nose") "add a nose"  (nose? #true)]
              [("-e" "--eyes") char "use <char> for the eyes" (eyes char)])

(printf "~a~a~a\n"
        (eyes)
        (if (nose?) "-" "")
        (if (smile?) ")" "("))

The library parses long and short flags, handles arguments, allows combining short flags, and handles -h and --help automatically:

$ racket /tmp/c -nfe 8
8-(