How to match the first word after an expression with regex?

regex lookbehind word-boundary
Matthew Taylor picture Matthew Taylor · Feb 13, 2009 · Viewed 73.3k times · Source

For example, in this text:

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc eu tellus vel nunc pretium lacinia. Proin sed lorem. Cras sed ipsum. Nunc a libero quis risus sollicitudin imperdiet.

I want to match the word after 'ipsum'.

Answer

Ben Blank picture Ben Blank · Feb 13, 2009

This sounds like a job for lookbehinds, though you should be aware that not all regex flavors support them. In your example:

(?<=\bipsum\s)(\w+)

This will match any sequence of letter characters which follows "ipsum" as a whole word followed by a space. It does not match "ipsum" itself, you don't need to worry about reinserting it in the case of, e.g. replacements.

As I said, though, some flavors (JavaScript, for example) don't support lookbehind at all. Many others (most, in fact) only support "fixed width" lookbehinds — so you could use this example but not any of the repetition operators. (In other words, (?<=\b\w+\s+)(\w+) wouldn't work.)

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