Basic REGEX for cleaning and prepping data

Over the 15 years or so, I have used the PHP Framework CodeIgniter, Amongst many of its good features is its built in Form Validation Library.

Every now and then I need to write adhoc code, or help others to write or develop sections of their site, I happy to help friends in need.

Today though I have been doing a lot of CodeIgniter validation, with some extra ‘callbacks’ using regex/preg_match & preg_replace combos,

Note: This is not are Regex tutorial, just some basic common examples.

Basic Examples

Strip non-numeric characters from a string:

<?php

    $string = 'sheldon is not james bond 007';
    $numbers = preg_replace('/[^0-9]+/', '', $string);
    // returns '007';
?>

Strip all none numeric and alpha characters from a string:

<?php 
    $string = 'sheldon, Is james bond (007)';
    $numbers = preg_replace('/^([a-z0-9])+$/i' '', $string); // the i means case insensitive.
    // returns 'sheldon Is james bond 007';
?>

Create a safe URL string:

Do you want to make url safe permalinks or strings?
Lets strip out anything that’ll break our address.

<?php 

    // assume $_POST['name'] = "sheldon's wonderful *product* costs $19.95";
    $name = str_replace(' ', '-', trim($_POST['name']));
    $url = preg_replace('/^([a-z0-9-_])+$/i', '', $name);

    header("Location: http://sheldon.lendrum.co.nz/". $url);
    //  http://sheldon.lendrum.co.nz/sheldons-wonderful-product-costs-19.95
?>

preg_replace() & preg_match()

I have used preg_replace() to strip out the unwanted tags, but if you just want to validation against with out altering the users data, you can use preg_match().
Here is an example to make sure a user has only submitted a trough z and 0 trough 9 characters and spaces.

<?php
    // assume $_POST['name'] = "sheldon's wonderful *product* costs $19.95";
    if(preg_match('/^([a-z0-9\ ])+$/i',  $_POST['name'])) {
    	// valid data ( spaces are allowed. )
    	// case insative
    	echo('Validation Passed');
    } else {
    	// this was invalid data
    	echo('Please enter a valid string.');
    }
?>

In this example, our string would fail.

We allowed spaces in our test, to run the same match with out allowing spaces, re can remove the ‘\ ‘ form the Regex.

Here is an example to make sure a user has only submitted a trough z and 0 trough 0 characters .

<?php
    // assume $_POST['name'] = "sheldon";
    if(preg_match('/^([a-z0-9])+$/i',  $_POST['name'])) {
	    // valid data ( spaces are  NOT allowed. )
    	// case insative
	    echo('Validation Passed');
    } else {
	    // this was invalid data
	    echo('Please enter a valid string.');
    }
?>

In this example, our post data would pass the validation – WIN!