Thankfully since then, the PHP community has embraced the PCRE functions which are more efficient and are Perl-compatible. However the downside to PCRE (and POSIX for that matter) is that you need to know regular expressions, which for a newbie to learn can feel like walking through a minefield.

Recently though the Filter Functions have become a very popular method to validate data. This is due to their small learning curve.

How to use the Filter Functions

In this example (Using the filter_var() function) the filter function takes the data you input (For example: email@example.com) and will return either the data (if it’s valid) or false (if the data is not valid).

<?php
// Filter an Email Address
var_dump(filter_var('email@example.com', FILTER_VALIDATE_EMAIL)); // Returns: string(17) "email@example.com"

// This is a fake email being filtered.
var_dump(filter_var('fake_mail.com', FILTER_VALIDATE_EMAIL)); // Returns: bool(false)

var_dump(filter_var('ema(i)l@e\xample.com', FILTER_SANITIZE_EMAIL )); // Returns: string(17) "email@example.com"

// Filter a URL
var_dump(filter_var('example.com', FILTER_VALIDATE_URL)); // Returns: bool(false)

// Filter a URL
var_dump(filter_var('http://example.com', FILTER_VALIDATE_URL)); // Returns: string(18) "http://example.com"

// Example usage
$email = 'email@example.com'; // or something submitted from a form.
if(!filter_var($email, FILTER_VALIDATE_EMAIL)){ // If this returns false
	die('The email you send is invalid.');
}
?>

A handful of the useful available filters are:

• FILTER_SANITIZE_STRING – Removes HTML tags and possibly unwanted characters.
• FILTER_SANITIZE_EMAIL – Removes unwanted characters from an email address.
• FILTER_SANITIZE_URL – Removes unwanted characters from a URL.
• FILTER_SANITIZE_NUMBER_INT – Returns only digits,  + and -.
• FILTER_VALIDATE_INT – If data is not an integer it will return false.
• FILTER_VALIDATE_URL – If data is not a URL it will return false.
• FILTER_VALIDATE_EMAIL – If data is not an email it will return false.
• FILTER_VALIDATE_IP- If data is not an IP it will return false.

function shorten_url($url, $service=NULL){
		if($service== 'tinyurl'){return get_link('http://tinyurl.com/api-create.php?url='.urlencode($url));}
		elseif($service == 'urly'){return get_link('http://ur.ly/new.txt?href='.urlencode($url));}
		elseif($service == 'isgd'){return get_link('http://is.gd/api.php?longurl='.urlencode($url));}
		elseif($service == 'klam'){return get_link('http://kl.am/api/shorten/?format=text&url='.urlencode($url));}
		elseif($service == 'unu'){return get_link('http://u.nu/unu-api-simple?url='.urlencode($url));}
		else{return get_link('http://api.tr.im/v1/trim_simple?url='.urlencode($url));}
		return $url;
	}

	function get_link($url){
		if(function_exists('curl_init')){
			$ch = curl_init();
			curl_setopt($ch, CURLOPT_VERBOSE, 1);
			curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
			//curl_setopt($ch, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);
			//curl_setopt($ch, CURLOPT_POST, 1);
			curl_setopt($ch, CURLOPT_URL, $url);
			$result = curl_exec($ch);
			$resultArray = curl_getinfo($ch);
			if ($resultArray['http_code'] == 200){
				return $result;
			} else {
				return FALSE;
			}
			curl_close($ch);
		}elseif(ini_get('allow_url_fopen') == 1){
			return fopen($url, 'r');
		}
		return FALSE;
	}

/* Usage */
echo shorten_url('http://www.fullondesign.co.uk/');
// returns: http://tr.im/JPCz

<?php
echo realpath('../');
// Would return: /home/mike/www/blogposts
?>

How to make a great example?

Here is the code so you can shorten strings and check for potentially embrassing words.

<?php
// String Cleaner - Cleans words you don't want out of strings.

// Step 1 - Define the string and the words yoiu want to remove.
$string = 'this is my silly input how cool is it?';
$words_to_remove ='silly|my|eggs'; // Seperate words with | this is regular expression.

// Step 2 - shorten the string
$string = substr($string, 0, 23); // This with return the first 23 characters (including spaces) in the string.

// Step 3 - Remove the words
echo preg_replace('#\b('.$words_to_remove.')\b#is', '', $string); // This will remove the 

// This would return:
// this is input
?>