If your existing array is potentially huge, maybe a binary search would be helpful. I implemented (a lame) one lately. I say lame because it does only eq and lt comparisons.

I keep meaning to rewrite this more like sort to take a comparison coderef.

But anyway, the code:

#! /usr/bin/perl -w

use strict;


{
   # Need integer division here.
   use integer;

   # Determine if a string exists in a sorted list of strings 
   # using a binary search
   # Fail to send a sorted list to this sub at your own peril
   sub listContains($$) {
      my ($list, $word) = @_;

      my $min = 0;
      my $max = $#$list;
      my $i = ($max - $min) / 2;

      my $done = 0;
      while (!$done) {
         my $current = $list->[$i];

         # Found it, return true
         return 1 if ($word eq $current);

         # Cut off half of the remaining list
         ($word lt $current) ? $max = $i : $min = $i;
         my $newi = $min + (($max - $min) / 2);

         # Out of list words to try
         $done = 1 if($newi == $i);

         $i = $newi;
      }

      # If we got here, the word was not found, return false
      return 0;
   }
}

# unsorted list
my @words = qw{
   icebox jakfruit kelvin liquid 
   effluvia fenestrate ghoul hufflepuff 
   yurt zoroastrian
   magnanamous necrosis ocular porridge
   albatross bolognese catharsis denigrate 
   unresponsive versimilitude wrangler xenophobic
   quayside runcible seriatim tangential
};
@words = sort @words;

my $word = shift;
print "$word: " . listContains(\@words, $word) . "$/";
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