Check if string is an MD5 Hash

I accidentally stopped hashing passwords before they were stored, so now my database has a mix of MD5 Passwords and unhashed passwords.

I want to loop through and hash the ones that are not MD5. Is it possible to check if a string is an MD5 hash?

You can check using the following function:

function isValidMd5($md5 ='')
{
    return preg_match('/^[a-f0-9]{32}$/', $md5);
}

echo isValidMd5('5d41402abc4b2a76b9719d911017c592');

The MD5 (Message-digest algorithm) Hash is typically expressed in text format as a 32 digit hexadecimal number.

This function checks that:

1. It contains only letters and digits (a-f, 0-9).
2. It's 32 characters long.

Maybe a bit faster one:

function isValidMd5($md5 ='') {
  return strlen($md5) == 32 && ctype_xdigit($md5);
}