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regexlookbehind

whitespaces inside positive lookbehind regex

wont work, how to fix this problem? I need to get the number. Foo can bee with space or without space.

(?<=Foo:\s?</b>).+\d
<b>Foo:</b>2013<br><b>Bar:</b>
<b>Foo: </b>2013<br><b>Bar:</b>
Solution

  • The problem is that variable length lookbehind are not allowed in many languages, however some languages allow to put alternatives inside:

    If you don't use Python or javascript, try this:

    (?<=Foo:\s</b>|Foo:</b>).+\d

    If you use Perl or PHP you can do this too:

    Foo:\s?</b>\K.+\d

    (but the difference in this second pattern is that Foo:\s?</b> are matched and remove from the match result. Thus if you need to match these characters before you can't use this way)