Tony's Regex Blog

Regular Expression Super Hero

2007-01-17T00:01:00Z

http://www.xkcd.com/c208.html

xkcd has many great comics, although this is the only regex one that I know of.

PDF of Regular Expression Pocket Reference

2007-01-16T03:33:00Z

O'Reilly decided to release all of their pocket references as PDFs. You can get a copy of the Regex Pocket Reference for $4.99.

I've really liked the trend of releasing books in PDF, especially references, because it means I can travel with my reference library on my laptop.

Write Your Own Regex Engine

2005-05-18T13:10:00Z

Just ran across a Mark-Jason Dominus article on writing your own regex engine. Reading the article and just contemplating writing the code is enough to give you insight into how regex engines work. And the more you know about regex engines the less often you'll be surprised by their behavior =)

For non-Perl users, it's worth checking out the Perl community's regex knowledge base. They've got a long history of regex use and struggle (and everyone seems to have copied their regex implementation). Mark-Jason's writings are one good place to start. His regex talk is one of the best. The talk's not free, but he's been nice enough to put the slides up.

Where's the whitespace?

2004-03-13T01:03:00Z

I'm really sad that Perl didn't solve the issue of regex readability before regex popularity exploded across every other programming language. Unreadable regular expressions have become a cross-cultural norm. Unfortunately Perl 6, which will have the extended whitespace feature enabled by default, will be released two years too late.

Fortunately for the brave few willing to break with tradition, you can easily add white space to your regular expressions. Every programmer alive already adds whitespace to every other programming language. I doubt anyone finds the regular expression syntax so verbose and readable that whitespace has become obsolete.

Here's how you add whitespace to various languages:

Perl: m/pattern/x

java.util.regex: Pattern.COMMENTS or the x modifier

.NET: IgnorePatternWhitespace or the x modifier

Python: X or VERBOSE

PHP: /pattern/x

Javascript: Doesn't support it but who cares. You can get around it with this:

var phone regex = 
       "\\d\\d\\d"    // area code
    + "\\d\\d\\d-"    // prefix
    + "\\d\\d\\d";    // exchange

I've got more to say about the importance of whitespace in my article, Five Habits for Successful Regular Expressions and in some slides from my talk Regular Expression Best Practices.