To find the longest substring shared by two strings.
sub longest_common_substr {
  # provided you know there are no NULs
  my $str = join "\0", @_;
  my $len = 1;
  my $match;

  while ($str =~ m{ ([^\0]{$len,}) (?= [^\0]* \0 [^\0]*? \1 ) }xg) {
    $len = length($match = $1) + 1;
  }

  return $match;
}

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In reply to Longest common substring by japhy

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