regexp to match xxx.xxx.xxx?

Question

I need to check input with preg_match, which must be of this format: xxx.xxx.xxx The number of block can vary... These are all examples of valid inputs:

001
00a.00a
0fg.001
aaa.aaa.001
001.001.002.001.001.001

Well I could probably write a regexp something like:

^([\da-z]{3}\.?)+$

But here comes the problem with the quantifier of the period. I mean if I use '?' to match 0 or 1 times, it would also match even if skip the dots somewhere, eg:

000.001.0010az001

then, if I used {1} to match one time, it would match nothing, because the last block does not have a dot.

So I can't think what to think of... Please advice

Answer 1

You can use:

^[\da-z]{3}(?:\.[\da-z]{3})*$