Question

I really don’t understand regular expressions and was wondering what the following regular expressions do. I want my address and name to accept ., - and alphanumerics.

Will this work or is there need for improvement? Plus if someone can break down the regular expressions '/^[A-Z0-9 \'.-]{1,255}$/i' so I can understand every part better.

Here is the php code.

if (preg_match ('/^[A-Z0-9 \'.-]{1,255}$/i', $_POST['address'])) {
    $address = mysqli_real_escape_string($mysqli, htmlentities($_POST['address']));
} else {
    echo '<p class="error">Please enter your address!</p>';
}

if (preg_match ('/^[A-Z0-9 \'.-]{1,255}$/i', $_POST['name'])) {
    $name = mysqli_real_escape_string($mysqli, htmlentities($_POST['name']));
} else {
    echo '<p class="error">Please enter your name!</p>';
}

Answer 1

Your pattern basically allowes any combination (between 1 and 255 characters) of the following: A-Z, 0-9, space, \, ‘, .

Decide for yourself if this is good enough.

As for your pattern:

/^[A-Z0-9 \'.-]{1,255}$/i 

The i at the end means it isnt case sensitive

/^[A-Z0-9 \'.-]{1,255}$/ 

The slashes denote the beginning and the end of the pattern

^[A-Z0-9 \'.-]{1,255}$

The ^ is the beginning and $ is the end of the string you look for

[A-Z0-9 \'.-]{1,255}

This allowes and combination of the characters between the brackets with 1 to 255 repetitions