My regular expressions arent working.

[Anon]

Im trying to make sure users only enter letters and numbers for their usernames (with the first character being only letters).

	if( !ereg("^[a-zA-Z0-9]", $reg_username) )
	{	
		template_header("$cfg_maintemplatefile");
		print($validatetxt[5]);
		template_footer("$cfg_maintemplatefile");
		exit;	
	}

	if( !(ereg("^[a-zA-Z]", substr($reg_username, 0, 1))) )
	{	
		template_header("$cfg_maintemplatefile");
		print($validatetxt[6]);
		template_footer("$cfg_maintemplatefile");
		exit;	
	}

People are able to still enter @#$#@$ and other characters. What's wrong with my code?

[Anon]

Your regexp only checks the first character, to see if it's a-z, A-Z or 0-9. To match what you want it to match you want to check the whole string, ie:

if(eregi("^{[a-z][a-z0-9]*$",} $reg_username))
{ ...valid username
}