Didier Stevens

Thursday 4 June 2015

Regular Expressions With Comments

Filed under: My Software — Didier Stevens @ 20:01

Many flavors of regular expressions support comments now. You can make your regular expression a bit more readable by adding comments. Like in programming languages, where a comment does not change the behavior of the program, a regular expression comment does not change the behavior of the regular expression.

A regular expression comment is written like this: (?#comment) where comment can be any text, as long it is not ).

Here is an example of a regular expression for a simple email address: [A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,6}

And here is the same regular expression with a comment (bold): [A-Z0-9._%+-]+@(?#domain)[A-Z0-9.-]+\.[A-Z]{2,6}

Why am I posting this? Because I’m using this in my new Snort rules I’m blogging about soon.

3 Comments »

  1. I’ve often thought that it would be good to have a verbose regular expression language that was very readable. It should translate directly into the usual terse regex and vice-versa.

    Comment by lseltzer — Friday 5 June 2015 @ 1:20

  2. Actually, you can put comments in regex to make them more unreadable than they already are …

    Comment by s — Friday 5 June 2015 @ 9:38

  3. 100% of the features can be abused …

    Comment by Didier Stevens — Friday 5 June 2015 @ 16:34


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