You could try using a regular expression:

#!/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";
    }
}
[download]

prints out:

An integer: 55
An integer: 255
An integer: 123
Not an integer: #123
Not an integer: $123
[download]

Can you show some examples of integers with $ and #, along with some code that you've tried?