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regexhardcodedcharacter-class

Reusing a character class in a regular expression

In order to keep a regular expression more brief, is there a shorthand way to refer to a character class that occurs earlier in the same regular expression?

Example

Is there a way to shorten the following:

[acegikmoqstz@#&].*[acegikmoqstz@#&].*[acegikmoqstz@#&]

Solution

  • Keep in mind that regex features are dependant on the language being used.

    With Java, you can do this:

    [acegikmoqstz@#&](?:.*[acegikmoqstz@#&]){2}

    But that's all, with java you can't refer to named subpattern.

    With PHP you can do that:

    (?(DEFINE)(?<a>[acegikmoqstz@#&]))\g<a>(?:.*\g<a>){2}