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Editorial Team
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Asked: 2026-05-29T11:18:05+00:00

I would like a regular expression that, starting at the beginning of the text,

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I would like a regular expression that, starting at the beginning of the text, matches a word. If the exact word is typed it matches, but will also match a certain minimal number of matching characters, provided that any additional characters also match.

For example, if I am trying to match “San Francisco,” but am willing to accept the first five characters as sufficient to identify it uniquely in the domain:

  • Match: San Francisco
  • Match: San F
  • Match: San Fra
  • Match: San Franciscoblahblah
  • Fail: Boston
  • Fail: San Diego
  • Fail: San Fransisko
  • Fail: San Frano

This almost works, but incorrectly matches the last two:

^San Fr?a?n?c?i?s?c?o?

I’m using .NET regular expressions, but a solution in any language will do.

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1 Answer

  1. Editorial Team

    The issue you’re having is one of grouping. 

    ^San F(r(a(n(c(i(s(c(o)?)?)?)?)?)?)?)?

    The parentheses will make it so that ‘a’ being allowed is dependent on a preceding ‘r’, and so forth. It will still match on ‘San Frano’ and ‘San Fransisko’, but the matches will only be ‘San Fran’, similar to your ‘San Fransiscoblahblah’ case.

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