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

my @url = ( 'a2.xyz', 'c3.xy1', 'b1.xyz1', 'a3.xy11');

for (@url){
   $_ .= '.nota.url';

    / [a-c][1-3]
      [.]
      xy (:? z[1]? | 1 )
      [.]
      nota
      [.]
      url
    /xms ? print "$_ : OK\n" : print "$_ : NOK\n";
}
[download]

Output:
a2.xyz.nota.url : OK
c3.xy1.nota.url : OK
b1.xyz1.nota.url : OK
a3.xy11.nota.url : NOK
[download]