How to add in every link (a href) tag a rel attribute with the help of php? [closed]

Answer 1

$pat = <<<pattern
~(<a href="[^"]+")(><img src="[^"]+" alt="[^"]+" title="[^"]+" border="[^"]+" /></a>)~
pattern;
$html = preg_replace($pat, "\\1 rel=\"lightbox\"\\2", $html);

Answer 2

If all the pictures in $mydata do not have the "rel" attribute, then solution is simple

$mydata = str_replace('<img ', '<img rel="lightbox"', $mydata);

In other cases, only if ">" character does not appear in attribute values​​, this code works

function rel_adder( $matches ) {
    if ( strpos($matches[0], 'rel=') === false ) {
        return $matches[1].'rel="lightbox" '. $matches[2];
    } else {
        return $matches[0];
    }
}
$mydata = preg_replace_callback('#(<img )([^>]+)>#i', "rel_adder", $mydata);