#!/usr/bin/perl

# http://perlmonks.org/?node_id=1144184

use strict;
use warnings;

sub e
  {
  /\Guc*/gc or return 0;                     # rule 1. & 5.
  /\Ga/gc and return e();                    # rule 2.
  /\Gc+/gc;                                  # rule 5.
  /\Gd/gc and return e() && /\Gf/gc && e();  # rule 3.
  /\Gb/gc and return e();                    # rule 4.
  return 1;
  }
  
for (qw( u udufu uau uu uc ubu ucbuc uaau ua uauau uccc ))
  {
  print e() && /\G\z/ ? "matches" : "   fail", "  $_\n";
  }