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Editorial Team
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Asked: 2026-05-27T22:58:22+00:00

I’m looking to match all text in the format foo:12345 that is not contained

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I’m looking to match all text in the format foo:12345 that is not contained within an HTML anchor. For example, I’d like to match lines 1 and 3 from the following:

foo:123456

<a href="http://www.google.com">foo:123456</a>

foo:123456

I’ve tried these regexes with no success:

Negative lookahead attempt ( incorrectly matches, but doesn’t include the last digit )

foo:(\d+)(?!</a>)

Negative lookahead with non-capturing grouping

(?:foo:(\d+))(?!</a>)

Negative lookbehind attempt ( wildcards don’t seem to be supported )

(?<!<a[^>]>)foo:(\d+)

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1 Answer

  1. Editorial Team

    Regex is usually not the best tool for the job, but if your case is very specific like in your example you could use:

    foo:((?>\d+))(?!</a>)

    Your first expression didn’t work because \d+ would backtrack till (?!</a>) matches. This can be fixed by not allowing \d+ to backtrack, as above with help of an atomic/nonbacktracking group, or you could also make the lookahead fail in case \d+ backtracks, like:

    foo:((?>\d+))(?!</a>|\d)

    Altho that is not as efficient.

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