#!/usr/bin/perl -w
                                                                                
use strict;
my( $mask, $position )= @ARGV;
die "Usage:\n\t$0 MASK POSITION\n"
  unless $mask and $position and $position =~ /^\d+$/ and $position > 0;
                                                                                
opendir( DIR, "." ) or die "can't opendir '.' for read: $!";

my @files= do {
  my %h;
  sort { ($h{$b} ||= -M $b) <=> ($h{$a} ||= -M $a) }
  grep { /^$mask/o } readdir(DIR)
};

closedir( DIR ) or warn "error closing dir '.': $!";
                                                                                
print "Your file is: ", ($files[$position-1] || "not found"), "\n";