Example 11-5. examples/regex/is_roman_number.pl

#!/usr/bin/perl
use strict;
use warnings;

while (my $number = <STDIN>) {

    # This solution only check is the string consists of characters used in as Roman numbers
    # but does not check if the number is actually a valid number. (e.g. IVI is not valid)
    # I yet to see a definition on how to validate a Roman number.
    if (is_roman($number)) {
        print "Roman number\n";
    }
}

sub is_roman    { $_[0] =~ /^[IVXLCDM]+$/    }

sub is_roman2   { $_[0] =~ /^(M{0,4})(CM|CD|D?C{0,3})(XL|XC|L?X{0,3})(IV|IX|V?I{0,3})$/  }