I'm using perl flavored regexes in PHP with the preg_match function. I want to validate a key that is exactly 10 characters, with upper case alpha characters or numbers.
I have
preg_match( '/[^A-Z0-9]/', $key);
which finds invalid characters next to valid ones. In my limited knowledge, I tried
preg_match( '/[^A-Z0-9]{10}$/', $key);
which turns out to match all my test strings, even the invalid ones.
How do I specify this regular expression?
You've misplaced the ^ character which anchors the beginning of a string. /[^A-Z0-9]{10}$/ would match all files ending on 10 characters that are not uppercase letters and digits.
The correct RE would be:
preg_match( '/^[A-Z0-9]{10}$/', $key);
Explanation of the regexp:
^ - matches from the beginning of the string
[ - begin of a character class, a character should match against these. If a ^ is found straight after this [, it negates the match
A-Z - uppercase letters0-9 - digits] - end of a character class{10} - matches the previous character class 10 times$ - matches the string till the end