Hi monks,

I'm wondering if it's possible to have a single regex that accepts a string if it's one of the following:

a) letters only
b) letters plus underscore
c) letters with numbers
d) letters plus underscore plus numbers

Strings that contain purely numbers or numbers with underscores are unacceptable.

Thanks in anticipation :)

Update: Thanks! Funny, I kept thinking it must be done with two regexes. Btw, from Re: A single regex, I'm wondering if it would still be doable with a single regex with one more constraint added:

Maximally one underscore.

Update: Wow, regex is really quite an art and a science in itself. Thanks to all for helping :)

In reply to A single regex by kiat

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