Match First Sequence in Regular Expression?

[Christos Georgiou]

On Thu, 26 Jan 2006 14:09:54 GMT, rumours say that "Roger L. Cauvin"
<roger at deadspam.com> might have written:

>Say I have some string that begins with an arbitrary sequence of characters 
>and then alternates repeating the letters 'a' and 'b' any number of times, 
>e.g.
>
>"xyz123aaabbaabbbbababbbbaaabb"
>
>I'm looking for a regular expression that matches the first, and only the 
>first, sequence of the letter 'a', and only if the length of the sequence is 
>exactly 3.
>
>Does such a regular expression exist?  If so, any ideas as to what it could 
>be?

Is this what you mean?

^[^a]*(a{3})(?:[^a].*)?$

This fits your description.
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