agrep - Approximate General Regular Expression Pattern Matcher
The best available tools for approximate pattern matching are
glimpse and agrep, developed by Manber and Wu at
the University of Arizona, and available from
http://glimpse.cs.arizona.edu/.
Glimpse is a tool for building and using an index for searching
through file systems, while agrep (approximate general regular expression
pattern matcher) is a tool supporting text search with spelling errors.
Both programs are widely used and respected.