#!/usr/bin/perl -w 

use strict;

my @stuff = qw(1234 a12345 12345 12345z);

foreach my $num (@stuff) {
	unless ($num =~ /^\d{5,}/) {
		print "Not Valid: $num\n";
	} else {
		print "Valid: $num\n";
	}
}

##</code><code>##

/^\d{5,}\D+/ #invalidates all except "12345z"
/^\d{5,}|\D+/ #only "1234" invalid