Question

What does (?=.*[^a-zA-Z]) mean

I am a beginner in regex and not getting what does it mean .

Is it like, dot(.) means any character so .* means any character any number of times and [^a-zA-z] any one character except a-z and A-Z.
what string will match it?

Thanks,

Puneet

Answer 1

That is positive look ahead assertion.

That means that there are at least one symbol that is not a-ZA-Z to right from the point.

Example:

$ echo 12abc | grep -P '2(?=.*[^a-zA-Z])'
$ echo 12abc. | grep -P '2(?=.*[^a-zA-Z])'
12abc.

In the first line there are no not a-zA-Z after 2. And the line will not be shown.

In the second line I’ve added point to the end. Now there is a not a-zA-Z after 2. And the line will be found and shown.