Excluding Matches With Regular Expressions
Here's an interesting regex problem:
I seem to have stumbled upon a puzzle that evidently is not new, but for which no (simple) solution has yet been found. I am trying to find a way to exclude an entire word from a regular expression search. The regular expression should find and return everything EXCEPT the text string in the search expression.
For example, if the word fox was what I wanted to exclude, and the searched text was:
The quick brown fox jumped over the lazy dog.
... and I used a regular expression of [^"fox"] (which I know is incorrect) (why this doesn't work I don't understand; it would make life SO much easier), then the returned search results would be:
The quick brown jumped over the lazy dog.
Regular expressions are great at matching. It's easy to formulate a regex using what you want to match. Stating a regex in terms of what you don't want to match is a bit harder.
One easy way to exclude text from a match is negative lookbehind:
But not all regex flavors support negative lookbehind. And those that do typically have severe restrictions on the lookbehind, eg, it must be a simple fixed-length expression. To avoid incompatibility, we can restate our solution using negative lookahead: