well, since we are about to intercept @ARGV, we can expect string of '--help', may be '-help' or even short versions such as '-h' or '--h' (though the latter seems odd). with version 5.10 or newer, smart match comes handy. i'd take 'help' out from GetOptions(), and prior to calling it, intercept @ARGV and call help() if match found. i like to separate the whole message printing in its own sub for easy modification on the text.

$ cat ghosh.pl
#!/usr/bin/perl

use Getopt::Long;
my $abc;

@ARGV ~~ /^--?h(elp)?$/ && help();

GetOptions ("abc=s" => \$abc);
 
sub help {
    print "This is help message\n";
    exit;
}
 
if ($abc) { print qq(You have choosen "abc" as $abc\n) };
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now, the presence of either -h --h -help --help will trigger help message.

$ ./ghosh.pl --help
This is help message

$ ./ghosh.pl --abc --help
This is help message

$ ./ghosh.pl --abc -help
This is help message

$ ./ghosh.pl --abc -h
This is help message

$ ./ghosh.pl --abc --h
This is help message

$ ./ghosh.pl --abc abc -h
This is help message

$ ./ghosh.pl --abc abc
You have choosen "abc" as abc

$ ./ghosh.pl --h
This is help message

$ ./ghosh.pl -h --abc
This is help message
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