TRE is a lightweight, robust, and efficient POSIX compatible regexp matching library with some exciting features such as approximate matching.

The agrep tool is similar to the commonly used grep utility, but agrep can be used to search for approximate matches.

The agrep tool searches text input for lines (or records separated by strings matching arbitrary regexps) that contain an approximate, or fuzzy, match to a specified regexp, and prints the matching lines. Limits can be set on how many errors of each kind are allowed, or only the best matching lines can be output.

Unlike other agrep implementations, TRE agrep allows full POSIX regexps of any length, any number of errors, and non-uniform costs.