Perl: Regular Expressions

Overview of Regular Expressions
A regular expression is a set of characters that determine a pattern or template used to match, or substitute, against a string. Regular expressions were oririnally a UNIX thing, but they now are supported by many text editors, class libraries, scripting tools and IDEs (Interactive Development Environments) including Microsoft Visual C++.

Regular expression is abbreviated as regexp or regex. Plural forms are regexps, regexes, or regexen.

Regular expressions are a powerful way to match strings, much easier than using the 'indexOf' and 'substitute' function found in most programming languages. There are numerous things that can be done with regular expressions, some examples:

• Find and substitute on any pattern of text
• Determine if a string is the proper format be it date, decimal, etc...
• In a list grab all words that begin with A through E
• Find content between HTML tags
• Strip all HTML tags

For more detail about regular expressions:

• Regular Expressions Quick Reference
• Regular Expressions Examples

Regular expressions can look and be confusing. I tend to write a test script with just my regexp, just to see if it works properly, and I usually end up rewriting it numerous times. If you want to learn more about Regular Expressions, see the Perl documentation and the links at the bottom of this page.

I do not recommend the book Mastering Regular Expressions, from O'Reilly. I had the first edition. Perhaps the second edition is better. Nonetheless, I found it to be the only bad O'Reilly book I have. It is confusing, and is not written with the idea of explaining how to write working regular expressions that you can use. The book seems to be the “story of regular expressions” and how to implement them on a lower level, such as in a programming language. I learned more about regular expressions from O'Reilly's Learning Perl and Perl Cookbook.

Related Links:

Perl Manual - Regular Expressions
PERL FAQ - Regular Expressions
Steve Litt's PERLs of Wisdom : RegExps

gnu.regexp package for Java

String Matching and Replacing in JavaScript 1.2 — someone's local copy of an article that was in the now defunct Netscape DevEdge