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

check_int('55');
check_int(0xff);
check_int(123);
check_int('#123');
check_int('$123');

sub check_int {
    my $num = shift;
    if ($num =~ /\D/) {
        print "Not an integer: $num\n";
    }
    else {
        print "An integer: $num\n";
    }
}