Useful PHP regular expressions for web developers

Validate domain name Verify if a string is a valid domain name.

$url = "/";
if (preg_match('/^(http|https|ftp)://([A-Z0-9][A-Z0-9_-]*(?:.[A-Z0-9][A-Z0-9_-]*)+):?(d+)?/?/i', $url)) {
    echo "Your url is ok.";
} else {
    echo "Wrong url.";
}

Mark a word from a text This very useful regular expression find a specific word in a text, and mark it. Extremely useful for search results.

$text = "regex has become popular in web programming.";

$text = preg_replace("/b(regex)b/i", '<mark>1</mark>', $text);
echo $text;

Get all images from a 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);
	}
}

Remove repeated words (case insensitive)

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

Remove repeated punctuation

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

Matching a XML/HTML tag This simple function takes two arguments: The first is the tag you’d like to match, and the second is the variable containing the XML or HTML.

function get_tag($tag, $html) {
  $tag = preg_quote($tag);
  preg_match_all('{<'.$tag.'[^>]*>(.*?)</'.$tag.'>.'}',
                   $html,
                   $matches,
                   PREG_PATTERN_ORDER);

  return $matches[1];
}

Matching an HTML/XML tag with a certain attribute value This function is very similar to the previous one, but it allow you to match a tag having a specific attribute. For example, you could easily match <div id=”header”>

function get_tag( $attr, $value, $xml, $tag=null ) {
  if( is_null($tag) )
    $tag = 'w+';
  else
    $tag = preg_quote($tag);

  $attr = preg_quote($attr);
  $value = preg_quote($value);

  $tag_regex = "/<(".$tag.")[^>]*$attrs*=s*".
                "(['"])$value2[^>]*>(.*?)</1>/"

  preg_match_all($tag_regex,
                 $xml,
                 $matches,
                 PREG_PATTERN_ORDER);

  return $matches[3];
}

Matching hexadecimal color values Another interesting tool for web developers! It allows you to match/validate a hexadecimal color value.

$string = "#555555";
if (preg_match('/^#(?:(?:[a-fd]{3}){1,2})$/i', $string)) { 
echo "example 6 successful.";
}

Find page title This handy code snippet will find and print the text within the <title> and </title> tags of a html page.

$fp = fopen("/blogs","r"); 
while (!feof($fp) ){
    $page .= fgets($fp, 4096);
}

$titre = eregi("<title>(.*)</title>",$page,$regs); 
echo $regs[1];
fclose($fp);

Generating automatic smileys Another function used by WordPress, this one allow you to automatically replace a smiley symbol by an image.

$texte='A text with a smiley :-)';
echo str_replace(':-)','<img src="smileys/souriant.png">',$texte);

Remove carriage returns, line feeds and tabs

$text = str_replace(array("
", "
", "
", "	"), '', $text);

Clean up a sentence end that has no trailing space

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