gistfile1.txt

#!/usr/bin/perl

use 5.010;

use warnings;
use strict;

# Important:  This script will ONLY print the image links if both the thumbnail
# and original image are found.

# ---

my $string_base = '<a href="%u.jpg" class="fancybox" rel="gallery"><img src="%u-thumb.jpg" /></a>';
my $scandir = '/tmp/sjohnson/images/';

# ---

opendir(DIR, $scandir) || die "can't opendir $scandir: $!";

# scan all files not matching ., .., or non 2-digit numerics
my @files = grep { $_ ne '.' && $_ ne '..' && m/^\d{2}/ } readdir(DIR);
closedir(DIR);

# a hash to just keep track of which 2 digit number codes we've seen
my %images_bank;

foreach (@files) {
  my $number_prefix = substr($_, 0, 2);

  if (! exists($images_bank{$number_prefix})) {
    if (-f "$scandir/$number_prefix.jpg" && -f "$scandir/$number_prefix-thumb.jpg") {

      # the 1 only means that "I've seen this number", it is not used for
      # anything other than just saying that I simply "saw it" already in the
      # hash table.
      $images_bank{$number_prefix} = 1;
    }
  }
}

my @image_numbers_by_seen = sort {$a <=> $b} keys %images_bank;

foreach my $number (@image_numbers_by_seen) {
  printf("$string_base\n", $number, $number);
}