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Editorial Team
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Asked: 2026-06-08T18:23:15+00:00

The following regex: $common_tlds = ‘us|me|com|net|org|ly|be|edu|gov|uk|ca|de|jp|fr|au|ru|ch|it|nl|se|no|es|mil|co’; $regex = ‘#(?:https?://)?([^.\s]+(?:[^\s.]|[^\s][^\s.])*\.(?:’ . $common_tlds . ‘)[^.\s]*)#i’; used

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The following regex:

$common_tlds = 'us|me|com|net|org|ly|be|edu|gov|uk|ca|de|jp|fr|au|ru|ch|it|nl|se|no|es|mil|co';

$regex = '#(?:https?://)?([^.\s]+(?:[^\s.]|[^\s][^\s.])*\.(?:' . $common_tlds . ')[^.\s]*)#i';

used here:

preg_replace($regex,'<a href="http://$1" target="_blank">$1</a>', $text);

Is giving me a PREG_BACKTRACK_LIMIT_ERROR on very short text. One example text is:

Life cant always give you the best shoes,handbags,clothes but it can give you the best creations.

I know, there are better link finding regex online, but I was curious about what in my regex was causing massive backtracking and how I could improve it. Thanks!

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1 Answer

  1. Editorial Team

    Try something like this:

    $regex = '#(?:https?://)?([^.\s]+(?:\.[^.\s]+)*\.(?:' . $common_tlds . '))#i';

    Comments:

    • You are seeing catastrophic backtracking – your pattern has too many ways to fail matching the string.
    • [^.\s]+(?:\.[^.\s]+)* allows only one way of matching the domain, anchoring at dots.
    • [^.\s]* – Removed from the end, not sure what it suppose to do after the tld. If you want to match domains like .co.il, you may want another dot there: (?:\.[^.\s]+)?
    • You may want a \b at the start, to avoid matching (google.com.
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