A simple PHP BBCode Parser function

php_bbcode_parser.php

<?php

/** 
* A simple PHP BBCode Parser function
*
* @author Afsal Rahim
* @link http://digitcodes.com/create-simple-php-bbcode-parser-function/
**/

//BBCode Parser function

function showBBcodes($text) {
	
	// NOTE : I had to update this sample code with below line to prevent obvious attacks as pointed out by many users.
	// Always ensure that user inputs are scanned and filtered properly.
	$text  = htmlspecialchars($text, ENT_QUOTES, $charset);

	// BBcode array
	$find = array(
		'~\[b\](.*?)\[/b\]~s',
		'~\[i\](.*?)\[/i\]~s',
		'~\[u\](.*?)\[/u\]~s',
		'~\[quote\](.*?)\[/quote\]~s',
		'~\[size=(.*?)\](.*?)\[/size\]~s',
		'~\[color=(.*?)\](.*?)\[/color\]~s',
		'~\[url\]((?:ftp|https?)://.*?)\[/url\]~s',
		'~\[img\](https?://.*?\.(?:jpg|jpeg|gif|png|bmp))\[/img\]~s'
	);

	// HTML tags to replace BBcode
	$replace = array(
		'<b>$1</b>',
		'<i>$1</i>',
		'<span style="text-decoration:underline;">$1</span>',
		'<pre>$1</'.'pre>',
		'<span style="font-size:$1px;">$2</span>',
		'<span style="color:$1;">$2</span>',
		'<a href="$1">$1</a>',
		'<img src="$1" alt="" />'
	);

	// Replacing the BBcodes with corresponding HTML tags
	return preg_replace($find,$replace,$text);
}

// How to use the above function:

$bbtext = "This is [b]bold[/b] and this is [u]underlined[/u] and this is in [i]italics[/i] with a [color=red] red color[/color]";
$htmltext = showBBcodes($bbtext);
echo $htmltext;

?>

Alert XSS

I've improved a little

public static function replaceBBcodes($text)
    {
    	$text = strip_tags($text);
		// BBcode array
		$find = array(
			'~\[b\](.*?)\[/b\]~s',
			'~\[i\](.*?)\[/i\]~s',
			'~\[u\](.*?)\[/u\]~s',
			'~\[quote\]([^"><]*?)\[/quote\]~s',
			'~\[size=([^"><]*?)\](.*?)\[/size\]~s',
			'~\[color=([^"><]*?)\](.*?)\[/color\]~s',
			'~\[url\]((?:ftp|https?)://[^"><]*?)\[/url\]~s',
			'~\[img\](https?://[^"><]*?\.(?:jpg|jpeg|gif|png|bmp))\[/img\]~s'
		);
		// HTML tags to replace BBcode
		$replace = array(
			'<b>$1</b>',
			'<i>$1</i>',
			'<span style="text-decoration:underline;">$1</span>',
			'<pre>$1</'.'pre>',
			'<span style="font-size:$1px;">$2</span>',
			'<span style="color:$1;">$2</span>',
			'<a href="$1">$1</a>',
			'<img src="$1" alt="" />'
		);
		// Replacing the BBcodes with corresponding HTML tags
		return preg_replace($find, $replace, $text);
	}

if url like this [url=https://ya.ru]test[/url]

'~\[url=([^"><]*?)\](.*?)\[/url\]~s',
and
'<a href="$1">$2</a>',