Regex for strings starting with letters/_ and (possibly) following letters/digits/_

Question

Why isn't this regex working for the string "Array a"?

let mutable line = "Array a"
let regexIdentifier = new Regex("^[a-zA-Z_][a-zA-Z0-9_]*$")   
line <- regexIdentifier.Replace(line, "\r\n$&\r\n")   //KEYWORDS separation
Console.WriteLine(line)   

(I want the program to separate both "Array" and "a" to different lines)

Answer 1

The whitespace in "Array a" isnt matched.

Better use a regexp like "^[\w_]+ [\w_]+$"