<"https://www.baidu.com";
if (preg_match('/^(http|https|ftp):\/\/([A-Z0-9][A-Z0-9_-]*("Your url is ok.";
} else {
 echo "Wrong url.";
}

<"Sample sentence from KomunitasWeb, regex has become popular in web programming. Now we learn regex. According to wikipedia, Regular expressions (abbreviated as regex or
regexp, with plural forms regexes, regexps, or regexen) are written in a formal language that can be interpreted by a regular expression processor";
$text = preg_replace("/(regex)/i", '<span style="background:#5fc9f6">1</span>', $text);
echo $text;

function get_the_title(){
  return 'Save the search.php file and open style.css. Append the following line to it: ';
}
$s = 'and php';
$title  = get_the_title();
$keys= explode(" ",$s);
$title  = preg_replace('/('.implode('|', $keys) .')/iu',
'<strong>\0</strong>',
$title);
echo $title;

<"|\')[^"\'>]+/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, $url);
 }
}
var_dump($images);

<"bbb<"
  [1]=>
  string(10) "aa<"
  [2]=>
  string(11) "ddd<"
 }
 [1]=>
 array(3) {
  [0]=>
  string(3) "bbb"
  [1]=>
  string(2) "aa"
  [2]=>
  string(3) "ddd"
 }
}
array(3) {
 [0]=>
 string(3) "bbb"
 [1]=>
 string(2) "aa"
 [2]=>
 string(3) "ddd"
}
*/