How to make a regex pattern that matches except if…

Short answer

We will take an example: match all /* ... */-type comments except when in string (in our example: JavaScript, so both single and double quotes will have to be excluded).

  1. Write the regex for what you want to match (later called m; our example: /\*.*?\*/1).
  2. Write the regular expressions for matching your exclusions (later called e1, e2, e3; our example: '[^']+' and "[^"]+").

Regex #1

  1. Write your final regex: e1|e2|(m) (our example: '[^']+'|"[^"]+"|(/\*.*?\*/)).
  2. Match group 1 instead of matching group 0.

Note: This requires code to parse the result. If you need something simple (sed? Which you would replace with a Perl command? Or just something you can use with match), see below.

Regex #2: alternative for Perl and PCRE (PHP)

  1. Write your final regex: (?:e1|e2)(*SKIP)(?!)|m (our example: (?:'[^']+'|"[^"]+")(*SKIP)(?!)|/\*.*?\*/).
  2. Match group 0 as usual.

Note: You can execute this expression as a Perl command: perl -pe '(?:\'[^\']+\'|"[^"]+")(*SKIP)(?!)|/\*.*?\*/'

You can test the regex and have it explained at this link.

Something more detailed

Continue reading How to make a regex pattern that matches except if…