When writing efficient regular expressions, one of the most important rules is: reduce the number of times the regexp engine starts a match, and then has to backtrack. Another important rule is: let the optimizer do the work. These rules may conflict. ;-)

\s*,\s* offers a lot of opportunity for backtracking. In principle, the engine can start matching at any place - although the optimizer will prevent that from happening. But still, it will match at places where there's a comma without a surrounding space. The longer regexp will only start matching at spaces and commas. However, the alteration may make it harder for the optimizer.

So, the only way to be sure it to benchmark. Using data (and perl version) that you'll be working on for real. As the data may actually decide which one is better.

In reply to Re: Comparing Regular Expressions by JavaFan
in thread Comparing Regular Expressions by vitoco

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