Question

I write regular expression for alphanumerics, but it is not taking space.
I want space (whitespace between characters).
I write like this:

^[a-zA-Z0-9_]*$

Answer 1

There is the \s escape sequence that mean “whitespace”.

Change you regex to this (adding whitespace to the list of characters):

^[a-zA-Z0-9_\s]*$

As noted by Alex, \w stands for word characters, so you could shorten it further:

^[\w\s]*$

See this handy cheat sheet.