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Asked: 2026-05-30T00:03:30+00:00

I’m trying to build a regular expression that will catch one of three patterns

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I’m trying to build a regular expression that will catch one of three patterns at the beginning of a string. I’ve figured out how to catch each pattern, but I haven’t figured out how to write a regular expression that will match on all three. Here are the patterns (each includes a space character at the end:

  • R[eE]:
  • R[eE]: \[a2geeks\]
  • R[eE]: \[a2geeks\] R[eE]:

I feel like there’s an elegant way to do this but I’ve been struggling with it for about an hour now. The best answer will also explain to me why it works.

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1 Answer

  1. Editorial Team

    This may do the job. The two groups enclosed in () are made optional by the ? (= one or more of the preceding expression). The final R[eE] is nested inside a larger () group since the middle pattern [a2geeks] needs to occur first.

    The ^ indicates that the pattern should be matched at the beginning of the string, and the .* at the ned matches the remainder of the string following this pattern.

    ^R[eE]:(\s\[a2geeks\](\sR[eE]:)?)?(.*)
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