As you know exactly where you want to match (at the end of string), you can first get length n of a word you are searching for, then using substr function get substring of length n of the word you are searching in and just do eq comparison of two strings:

#!perl -l

@array = ('own', 'known', 'owl');

$q = 'unknown';
$longestmatching = '';
$longestn = 0;
for $testword(@array)
{
  $n = length($testword);
  next if $n <= $longestn;
  
  $substr = substr($q, length($q)-$n, $n);
  if($testword eq $substr)
  {
    $longestmatching = $testword;
    $longestn = $n;
  }
}

print $longestmatching;
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Additionally you can do sort of @array from longest to shortest string as others mentioned.