I need a ruby regexp pattern that matches a string containing a letter (for simplicity say ‘a’) n times and then n at the end.
For example, it should match “aaa3”, “aaaa4” etc but not “a2” or “aaa1”, etc.
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I need a ruby regexp pattern that matches a string containing a letter (for simplicity say ‘a’) n times and then n at the end.
For example, it should match “aaa3”, “aaaa4” etc but not “a2” or “aaa1”, etc.
That is not possible in regex since it is not a regular language (that’s easy to prove with the Pumping Lemma for Regular Languages). I’m not sure how much more powerful ruby regex is than a true Regular Expression, but I doubt it’s powerful enough for this. You can set a finite limit on it and state each possibility like:
Since all finite lanugages are regular, but it would be much easy to use string operations to count the number of times a letter appears and then parse for that integer in the string right after the last of that letter.