Validating form data using regex

Question

I'm newest and happy to be here in Stackoverflow. I am following this website since a long time.

I have an input/text field. (e.g. "Insert your name")

The script starts the following controls when the user sends data:

1) Control whether the field is empty or not.

2) Control whether the field goes over maximum characters allowed.

3) Control whether the field contain a wrong matched preg_match regex. (e.g. it contains numbers instead of only letters - without symbols and accents -).

The question is: why if i put this characters "w/", the script doesn't make the control? And it seems like the string bypass controls?

---

Hello to all guys and sorry if I'm late with the answer (and also for the non-code posted ^^).

Now, talking about my problem. I checked that the problem is on ONLY if I work offline (I use EasyPhp 5.3.6.1). Otherwise the regEx tested online is ok.

This is the code I use to obtain only what I said above:

    if (!preg_match('/^[a-zA-Z]+[ ]?[a-zA-Z]+$/', $name)) {

         echo "Error";

    }

As you can see, this code match:

• A string that start (and finish) with only letters;
• A string with only 0 or 1 empty space (for persons who has two name, i.e.: Anna Maria);

...right?!

(Please correct me if I am wrong)

Thanks to all!

Wart

Answer 1

It works fine.

<?php
$string = '\with';
if (preg_match('~[^0-9a-z]~i', $string)){
    echo "only a-Z0-9 is allowed"; //true
}

http://sandbox.phpcode.eu/g/18535/3

You have to make sure you don't put user input into your regex, because that would mean you'll probably check something wrong.

Answer 2

My reading of the requirements is

• Only letters (upper or lower) can be provided.
• Something must be provided (i.e. a non-zero length string).
• There is a maximum length.

The code below checks this in a very simple manner and just echos any errors it finds; you probably want to do something more useful when you detect an error.

<?php

$max    = 10;
$string = 'w/';

// Check only letters; the regex searches for anything that isn't a plain letter
if (preg_match('/[^a-zA-Z]/', $string)){
    echo 'only letters are allowed';
} 

// Check a value is provided
$len = strlen($string);
if ($len == 0) {
    echo 'you must provide a value';
}

// Check the string is long to long
if ($len > $max) {
   echo 'the value cannot be longer than ' . $max;
}

Answer 3

You can also try this:

if (preg_match('/^[a-z0-9]{1,12}/im', $subject)) {
    \\ match
}

The above will only match similar to @genesis' post, but will only match if the $subject is between and including 1 - 12 characters long. The regex is also case insensitive.