#! /usr/local/bin/perl -w
#LongestMatch.pl
#from Friedl: Mastering Regular Expressions, pp. 334-335

use strict;

my $longest_match = undef; # We'll keep track of the longest match here

my $RecordPossibleMatch = qr{
   (?{
      # Check to see if the current match ($&) is the longest so far
      if (not defined($longest_match)
          or
          length($&) > length($longest_match))
      {
          $longest_match = $&;
      }
   })
   (?!) # Force failure so we'll backtrack to find further "matches"
}x;

while (<>) {
    chomp;

    $_ =~ m{  [abcdef]{0,1} 
              [gh]{0,1}
              [ij]{0,1}
              [klmn]{0,1}
              [op]{0,1}
              [qr]{0,1}
              [astuv]{0,1}
              [gh]{0,1}
              [wxyz]{0,1}
              $RecordPossibleMatch  }x;

    # Now report the accumulated result, if any
    if (defined($longest_match)) {
       print "$longest_match\n";
    } else {
       print ".\n";
    }
    $longest_match = undef;
}