How to validate pattern in input string?

Question

If I had a webpage and I neeed to ensure user input for a variable is only letters (upper and lower), numbers and dashes and the length had to be exactly 20 chars in length, how would one perform that?

Answer 1

This is pretty easy to do using regular expressions:

echo preg_match('/^[0-9a-zA-Z\-]{20}$/', 'abcd');
0
echo preg_match('/^[0-9a-zA-Z\-]{20}$/', 'abcdefghijkmlnopqrst');
1