Repeated Capturing Group

Ethan — Sat, 04 Apr 2020 00:00:00 +0000

Regular expression can be used to check a string or a pattern is repeated in a string. For example, if you want to check if the string 'abc' is repeated for exactly 3 times in a string, you can use the following regex: (abc)\1{2}, or it would be like this in Java after adding the escape characters:

Pattern.compile("(abc)\\1{2}");

The \1 in the regex matches the first capturing group in the regex. If you want it to match the second capturing group, you can use \2 and so on.

It is also possible check if a capturing group is repeated at least n times or more than n times. For examples,

to check if abc is repeated in a string for at least 5 times, (abc)\1{4,}
to check if abc is repeated in a string for less than 5 times, (abc)\1{0,4}

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Repeated Capturing Group