Text::Soundex - Implementation of the Soundex Algorithm as Described by Knuth


  use Text::Soundex;

  $code = soundex $string;    # get soundex code for a string
  @codes = soundex @list;     # get list of codes for list of strings

  # set value to be returned for strings without soundex code

  $Text::Soundex::nocode = 'Z000';


This module implements the soundex algorithm as described by Donald Knuth in Volume 3 of The Art of Computer Programming. The algorithm is intended to hash words (in particular surnames) into a small space using a simple model which approximates the sound of the word when spoken by an English speaker. Each word is reduced to a four character string, the first character being an upper case letter and the remaining three being digits.

The value returned for strings which have no soundex encoding is set in the scalar $Text::Soundex::nocode. This is initially set to undef, but many people seem to prefer an unlikely value like Z000 (how unlikely this is depends on the data set being dealt with.) Any value can be assigned to $Text::Soundex::nocode.

For backward compatibility with older versions of this module the $Text::Soundex::nocode is exported into the caller's namespace as $soundex_nocode.

In scalar context soundex returns the soundex code of its first argument, and in array context a list is returned in which each element is the soundex code for the corresponding argument passed to soundex e.g.

  @codes = soundex qw(Mike Stok);

leaves @codes containing ('M200', 'S320').


Knuth's examples of various names and the soundex codes they map to are listed below:

  Euler, Ellery -> E460
  Gauss, Ghosh -> G200
  Hilbert, Heilbronn -> H416
  Knuth, Kant -> K530
  Lloyd, Ladd -> L300
  Lukasiewicz, Lissajous -> L222


  $code = soundex 'Knuth';         # $code contains 'K530'
  @list = soundex qw(Lloyd Gauss); # @list contains 'L300', 'G200'


As the soundex algorithm was originally used a long time ago in the US it considers only the English alphabet and pronunciation.

As it is mapping a large space (arbitrary length strings) onto a small space (single letter plus 3 digits) no inference can be made about the similarity of two strings which end up with the same soundex code. For example, both Hilbert and Heilbronn end up with a soundex code of H416.


This code was originally implemented by Mike Stok ( as an example of unreadable perl 4 code and refined into a library. Mark Mielke <> recast the code and made it much more speedy in 1997.

Ian Phillips ( and Rich Pinder ( supplied ideas and spotted mistakes.