$ 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) };

##</code><code>##

$ ./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