#!/usr/bin/perl

use strict;

my %fill = (
    #'M(ary)'  => 'G\1',
    'M(ary)'  => 'G$1',
);

while (my $line = (<DATA>)) {
    foreach my $key (keys %fill) {
        if ($line =~ /$key/) {
            $line =~ s/$key/$fill{$key}/;
        }
    }
    print "$line";
}

__DATA__
Mary has a little lamb