ulferik

I don't really see anything that's wrong. Try adding more output to the login() function, which is currently very compact. Store the generated SQL query in a variable, and print it on the screen before running it. Store the returned COUNT(*) value in a variable, and print that too on the screen. Then you'll see what's going on.

I'd suggest to construct the new contents of the file and store it with a temporary filename, and only switch it over to the real name when it's finished.

Try storing it in a session.

Don't know the answer, but you have a security vulnerability in line #2.