#!/usr/bin/perl

# https://perlmonks.org/?node_id=1216404

use strict;
use warnings;
use Search::Dict;

my $file = join "", sort <DATA>;
open my $handle, '<', \$file or die;

for my $argument ( 11673326, 11673335, 11673321 )
  {
  0 <= look $handle, $argument + 1 or die "look error";
  print "next after $argument is ", <$handle> // "undefined\n";
  }

__DATA__
11673326
11673329
11673325
11673330
11673321
11673335
[download]

Outputs:

next after 11673326 is 11673329
next after 11673335 is undefined
next after 11673321 is 11673325
[download]