regular expressions to validate username (allow only letters and _ )

[Vivid Lust]

Could someone please help me with regular expressions?

 

I'm writing a function to check if a username is valid, it can only contain letters and underscores, this is what i wrote:

 

	function isValidUsername($TargetUsername){
		if( !preg_match("/^[A-Za-z]_$/", $TargetUsername) ){
			return false;
		}else{
			return true;
		}
	}

Is it correct? It always returns false .. if for example, the input is "abc" it returns false which isnt what i want it to do ! Please help!! thanks.

[salathe]

Move the underscore (_) one character to the left and put a plus symbol (+) where it was. Then tell my why that would work.