my @ips = qw( 127.0.0.1 0.0.0.0 256.0.0.1 123.555.333.222666 ); foreach my $ip (@ips) { my $f = undef; if($ip =~ m/^(?!0+\.0+\.0+\.0) ([01]?\d\d?|2[0-4]\d|25[0-5]) \.([01]?\d\d?|2[0-4]\d|25[0-5]) \.([01]?\d\d?|2[0-4]\d|25[0-5]) \.([01]?\d\d?|2[0-4]\d|25[0-5])$/x ) { $f =1; } print 'Is', $f ? "" : 'n\'t', " valid and/or usable IP: $ip \n" } #### Is valid and/or usable IP: 127.0.0.1 Isn't valid and/or usable IP: 0.0.0.0 Isn't valid and/or usable IP: 256.0.0.1 Isn't valid and/or usable IP: 123.555.333.222666