#!/usr/bin/perl -w
                                                                                
use warnings;
use strict;
no strict 'refs';
                                                                                
our $a = 10;
our $b = 20;
our $c = 33;
our $d = 123;
                                                                                
my @lines = qw( <:a:0:> <:a:3:> <:b:0:> <:b:4:> <:c:5:> <:d:6:> );
                                                                                
foreach my $line (@lines) {
    if ($line =~ s/<:(\w+):(\d+):>/$$1*($2||1)/e) {
        printf "Result = %d\n", $line;
    }
}