GNU awk User's Guide - Regular Expressions
Documentation of the Regular Expression syntax used in GNU Awk.
grep - Regular Expressions
Documentation of the Regular Expression syntax used in GNU grep.
Learning to Use Regular Expressions by Example
A tutorial at phpbuilder.com.
Mastering Regular Expressions (Second Edition)
Book by Jeffrey Friedl. Includes table of contents, full index, an errata sheet.
MSDN .NET Regular expressions
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpgenref/html/cpconRegularExpressio
MSDN documentation on .NET regular expressions.
Posix Basic Regular Expression
A description of both basic Posix Regular Expression syntax, the programming interface and some advanced features that are provided in the implementation of POSIX.2 regular expressions in the GNU C Library.
Programming in Emacs Lisp - Regular Expression Sea
Documentation of the Regular Expression syntax used in Emacs Lisp.
RE Tool
Java based cross platform tool to learn Regular Expressions by "Trial & Error". Comes with Regular Expressions reference.
Regular Expression Features in Tcl 8.1
A HowTo guide for the Regular Expression Features contained in Tcl 8.1.
Regular Expression HOWTO
Detailed HowTo documentation about regular expressions usage in combination with the Phyton programming/scripting language.
Regular Expression Quick Reference
Tried and tested, single sheet quick reference card for regular expressions. [PDF file]
Regular Expressions
A brief and general introduction.
Regular expressions
An introduction from a University course.
Regular Expressions - Single Unix Specification
Specification for regular expressions -- massive document, somewhat technical.
Regular Expressions HOWTO The Basics of REReplace
By Pete Freitag. The basics of using regular expressions with ColdFusion's REFind, and REReplace functions.
Regular Expressions in ne (Nice Editor)
A description of the regular expression support in ne (Nice Editor).
Regular expressions in UNIX (Spring 1995)
Slightly inaccurate (mixes in glob patterns and calls them "shell regular expressions") but otherwise a good concise summary of plain vs extended regular expressions.
Regular Expressions Reference
Downloadable reference with examples, by Miloslav Nic.
Regular Expressions Tutorial
A tutorial and reference for many popular regular expression flavors used by programming languages like Perl, PHP, Java, C# and VB.NET as well as a description of general tools like PowerGREP and EditPad.
Regular Expressions Tutorial at Zvon
A tutorial with many examples which can be downloaded for off-line use.
Regular Expressions: An Introduction
An essential guide to one of the most useful tools in the web development: regular expressions.
Seeing With C - Regular Expressions
A writeup on regular expressions connecting the math. and the CS views to regular expressions.
The Regular Expression Rundown
A short description of Regular Expressions.
Unicode Regular Expression Guidelines
Unicode Technical Report #18: This document describes guidelines for how to adapt regular expression engines to use Unicode.
Using Regular Expressions
Good overview of regular expression operators, although some features described might not be available in your implementation.