7.2.69 Text::Soundex - The Soundex Algorithm 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
$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 that 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 uppercase letter and the remaining three being digits.

If there is no soundex code representation for a string, then the value of $soundex_nocode is returned. This variable is initially set to the undefined value, 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 $soundex_nocode.

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

For example:

@codes = soundex qw(Mike Stok);

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

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

So we have:

$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 United States, 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 three digits), no inference can be made about the similarity of two strings that end up with the same soundex code. For example, both Hilbert and Heilbronn end up with a soundex code of H416.