Regex Performance Optimization Tips and Tricks

Question

After reading a pretty good article on regex optimization in java I was wondering what are the other good tips for creating fast and efficient regular expressions?

Answer 1

I suggest you to read the book Mastering Regular Expressions by Jeffrey Friedl.

Answer 2

Use the any (dot) operator sparingly, if you can do it any other way, do it, dot will always bite you...

i'm not sure whether PCRE is NFA and i'm only familiar with PCRE but + and * are usually greedy by default, they will match as much as possible to turn this around use +? and *? to match the least possible, bear these two clauses in mind while writing your regexp.

Answer 3

Know when not to use a regular expression -- sometimes a hand coded solution is more efficient and more understandable.

Example: suppose you want to match an integer that's evenly divisible by 3. It's trivial to design a finite state machine to accomplish this, and therefore a corresponding regex must exist, but writing it out is not so trivial -- and I'd sure hate to have to debug it!