Question

I want a regular expression which ALLOWS only this:

 letter a-z
 case insensitive
 allows underscores
 allows any nrs

How should this be written?

Thanks

Answer 1

That would be

\w

if I’m not mistaken (As it turns out, it depends: In PHP the meaning of \w changes with the locale that’s currently in effect). You can use a more explicit form to nail it down:

[A-Za-z0-9_]

I use it in context, add start-of-string and end-of-string anchors and a quantifier that defines how many characters you will allow:

^[A-Za-z0-9_]+$