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Processing Command-Line Options With Perl
Add support for command-line options to your Perl program.

| Down To Work |

Now, with the hard sell out of the way, let's get down to the nitty-gritty of how Getopt::Long.pm works. Consider the following simple example:


#!/usr/bin/perl

# import module
use Getopt::Long;

# set default value for option
$debug = 0;

# get value of debug flag
$result = GetOptions ("debug" => \$debug); 
                 
# print value
print "Debug flag is $debug";


Now, try running this code as is:


$ ./script.pl
Debug flag is 0


And then try running it after adding a "--debug" command-line option:


$ ./script.pl --debug
Debug flag is 1


As you can see, the Perl code now recognizes the "--debug" flag on the command line, and sets a Boolean variable to true within the script.

Most of the magic here lies in the call to the GetOptions() function. This function accepts a series of option-variable pairs, demarcated using standard hash notation and separated with commas. When GetOptions() is called, it reads the program command line, looks for matching arguments, and if found, sets the corresponding option variable to true. Thus when you call the Perl script above with the "--debug" option, GetOptions() recognizes it and automatically sets the $debug variable to true.

You can set more than one option variable at a time as well - consider the following example and its output, which demonstrates:


#!/usr/bin/perl

# import module
use Getopt::Long;

# read options
$result = GetOptions (   "red" => \$red,
            "blue" => \$blue,
            "green" => \$green ); 
                 
# print options
$red ? print "Red is present\n" : print "Red is absent\n";
$blue ? print "Blue is present\n" : print "Blue is absent\n";
$green ? print "Green is present\n" : print "Green is absent\n";


Here's an example of the output:


$ ./colors.pl  --red --blue
Red is present
Blue is present
Green is absent



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