Author image Vaclav Barta
and 1 contributors


Algorithm::AhoCorasick - efficient search for multiple strings


Version 0.03


 use Algorithm::AhoCorasick qw(find_all);

 $found = find_all($text, @keywords);
 if (!$found) {
     print "no keywords found\n";
 } else {
     foreach $pos (sort keys %$found) {
         $keywords = join ', ', @{$found->{$pos}};
         print "$pos: $keywords\n";


Aho-Corasick is a classic (1975) algorithm for locating elements of a finite set of strings within an input text. It constructs a finite state machine from a list of keywords, then uses the machine to locate all occurrences of the keywords. Construction of the machine takes time proportional to the sum of the lengths of the keywords and the machine processes the input string in a single pass - that is, the algorithm may be considerably more efficient than searching for each keyword separately.


The module exports 2 functions for the common use cases: find_all for finding all matches, and find_first for finding whether a match exists at all. Note that both functions must be explicitly imported (i.e. with use Algorithm::AhoCorasick qw(find_all find_first);) before they can be called. Both functions take the same arguments: the first argument is the text to be searched, the following are the keywords to search for (there must be at least one, and the functions die rather than search for empty strings).


When no keyword is found in the input text, find_all returns undef; when some keywords are found, the return value is a hash reference mapping positions to keywords (in an array reference, ordered by length) found at those positions.


When no keyword is found in the input text, find_first returns undef in scalar context and an empty array in list context; when a keyword is found, the return value is a pair of its position in the input text and the found keyword (as a list if the function has been called in list context, as an array reference otherwise).


find_all and find_first are just thin wrappers around the state machine class Algorithm::AhoCorasick::SearchMachine, which can also be used directly for a more customizable search scenarios (i.e. when the input text isn't available all at once) - see the Algorithm::AhoCorasick::SearchMachine POD for details.


Vaclav Barta, <>


Please report any bugs or feature requests to bug-algorithm-ahocorasick at, or through the web interface at I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


Copyright 2010 Vaclav Barta, all rights reserved.

This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.


Adapted from implementation by Tomas Petricek, available at .

The algorithm is from Alfred V. Aho and Margaret J. Corasick, Efficient string matching: an aid to bibliographic search, CACM, 18(6):333-340, June 1975.