I'm trying to make functions for validating usernames, emails, and passwords and my regex isn't working. My regex for usernames is ^[a-zA-Z0-9 _-]$ and when I put anything through that should work it always returns false.
As I understand it, the ^ and $ at the beginning and the end means that it makes sure the entire string matches this regular expression, the a-z and A-Z allows all letters, 0-9 allows all numbers, and the last three characters (the space, underscore, and dash) allow the respective characters.
Why is my regular expression not evaluating properly?
You need a quantifier, + or *. As it was written that only allows 1 of the characters in the character class.
Your a-zA-Z0-9_ also can be replaced with \w. Try:
^[\w -]+$
+ requires 1 or more matches. * requires 0 or more matches so if an empty string is valid use *.
Additionally you could use \h in place of the space character if tabs are allowed. That is the metacharacter for a horizontal space. I find it easier to read than the literal space.
Per comment, Update:
Since it looks like you want the string to be between a certain number of characters we can get more specific with the regex. A range can be created with {x,y} which will replace the quantifier.
^[\w -]{3,30}$
Additionally in PHP you must provide delimiters at the start and end of the regex.
preg_match("/^[\w -]{3,30}$/", $username);
Additionally, you should enable error reporting so you get these useful errors in the future. See https://stackoverflow.com/a/21429652/3783243