PCRE is a widely used Unicode-compatible regular expression engine. It implements Perl5 regex syntax and semantics, some Python, .NET and Onigurama extensions. It uses just-in-time compilation, has consistent escaping rules, and allows for recursion, assertions and conditional patterns or complex subroutines and callouts, thus goes far beyond classic regular expressions.
UniversalCodeGrep (ucg) is an extremely fast grep-like tool specialized for searching large bodies of source code. It is intended to be largely command-line compatible with Ack, to some extent with ag, and where appropriate with grep. Search patterns are specified as PCRE regexes.
sreplace is a simple command-line tool to search and replace text in files and across directory trees. It works with large files, can search with regular expressions, and even allows binary block substitution, or conver CR/LF linebreak variants, tabs or strip trailing spaces.
Command line based user interface for editing and applying python scripts that convert lines in a file or from stdin however the user wants it and by whatsoever method is available through python including regex, parsers, string manipulation, calling subprocesses and everything else.
grec is a search tool similar to grep. Instead of just matching text its purpose is colorizing output lines. By specifying a regex and a simple color name/scheme it can display matched results from e.g. a shell pipe. It takes care to not misinterpret distinct regex matches with colorization areas.