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O'Reilly Open Source Convention


Regular Expression Mastery
Mark-Jason Dominus, Plover Systems Co.

Track: Perl
Date: Tuesday, July 08
Time: 8:45am - 12:15pm
Location: Salon F

It can be hard to predict what a regex will do. Almost everyone has written a regex that failed to match something they wanted it to, or that matched something they thought it wouldn't. That will never happen to you again after you take this tutorial.

We will explore the algorithm that Perl uses internally to perform regex matching. Understanding this algorithm will allow us to predict whether a regex will match, which of several matches Perl will find, and which regexes will be faster than others. During this discussion we'll pause to discuss practical applications that illustrate features of the algorithm. We'll examine the essential but usually misunderstood concept of 'greed', and we'll learn why commonly-used regex symbols like '.', '$', and '\1' might not mean what you thought they did.

In the second section, we'll apply our knowledge of the internals, examining several common disasters, a few practical parsing applications, and some new features that would have been hard to understand before. We'll see an example of every regex metacharacter and modifier. We'll finish with a discussion of some of the new optimizations that were added in Perl 5.6, and why you should avoid the '/i' modifier.

Part I: Inside the Regex Engine. Regular Expressions are Programs; Backtracking; Quantifiers; Greed; Assertions; Backreferences.

Part II: Disasters and Optimizations. Where machines come from; Disaster examples; Regex modifiers; Tokenizing; New optimizations; Matching strings with balanced parentheses.

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