PHP preg_replace – some useful regular expressions

There loads of these all over the place, but here’s some useful preg_replace examples for text and html processing that were hard to find or I ended up writing  – use/praise/embellish/flame as you see fit.

Remove repeated words (case insensitive)

$text = preg_replace("/\s(\w+\s)\1/i", "$1", $text);

‘Keep your your head’ becomes ‘Keep your head’

 Remove repeated punctuation

$text = preg_replace("/\.+/i", ".", $text); 

 ‘Keep your head…’ becomes ‘Keep your head.’ Don’t forget to escape regex characters.

Clean up a sentence end that has no trailing space

$text = preg_replace("/\.(?! )/i", ". ", $text);

‘Keep your head.Don’t fall apart’ becomes ‘Keep your head. Don’t fall apart’  This uses lookahead.

Remove carriage returns, line feeds and tabs

$text = str_replace(array("\r\n", "\r", "\n", "\t"), '', $text);

An oldy but goody.

Get all image urls from an html document

$images = array();
preg_match_all('/(img|src)\=(\"|\')[^\"\'\>]+/i', $data, $media);
unset($data);
$data=preg_replace('/(img|src)(\"|\'|\=\"|\=\')(.*)/i',"$3",$media[0]);
foreach($data as $url)
{
	$info = pathinfo($url);
	if (isset($info['extension']))
	{
		if (($info['extension'] == 'jpg') ||
		($info['extension'] == 'jpeg') ||
		($info['extension'] == 'gif') ||
		($info['extension'] == 'png'))
		array_push($images, $url);
	}
}
Puts all the image URLs in an array

Strip non printable characters

$text = preg_replace("/[^[:print:]]+/", "", $text);

Does what it says on the tin

Remove HTML tags

$text = preg_replace
	(
	array(
	// Remove invisible content
	'@<head[^>]*?>.*?</head>@siu',
	'@<style[^>]*?>.*?</style>@siu',
	'@<script[^>]*?.*?</script>@siu',
	'@<object[^>]*?.*?</object>@siu',
	'@<embed[^>]*?.*?</embed>@siu',
	'@<applet[^>]*?.*?</applet>@siu',
	'@<noframes[^>]*?.*?</noframes>@siu',
	'@<noscript[^>]*?.*?</noscript>@siu',
	'@<noembed[^>]*?.*?</noembed>@siu',

	// Add line breaks before & after blocks
	'@<((br)|(hr))@iu',
	'@</?((address)|(blockquote)|(center)|(del))@iu',
	'@</?((div)|(h[1-9])|(ins)|(isindex)|(p)|(pre))@iu',
	'@</?((dir)|(dl)|(dt)|(dd)|(li)|(menu)|(ol)|(ul))@iu',
	'@</?((table)|(th)|(td)|(caption))@iu',
	'@</?((form)|(button)|(fieldset)|(legend)|(input))@iu',
	'@</?((label)|(select)|(optgroup)|(option)|(textarea))@iu',
	'@</?((frameset)|(frame)|(iframe))@iu',),

	array(
	' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ', ' ',
	"\n\$0", "\n\$0", "\n\$0", "\n\$0", "\n\$0", "\n\$0",
	"\n\$0", "\n\$0",),$text
	)
// Remove all remaining tags and comments and return.
$text = strip_tags( $text );

Ok, so strip_tags sort of does this, but fails to remove script, style etc etc.