PHP Substring of a regex replacement

Question

I have the following regex :

 $string = preg_replace("/([\w]+:\/\/[\w-?&;#~=\.\/\@]+[\w\/])/i","<a target=\"_blank\" href=\"$1\">$1</A>",$string);

Using it to parse this string : http://www.ttt.com.ar/hello_world

Produces this new string :

<a target="_blank" href="http://www.ttt.com.ar/hello_world">http://www.ttt.com.ar/hello_world</A>

So far , soo good. What I want to do is to get replacement $1 to be a substring of $1 producing an output like :

<a target="_blank" href="http://www.ttt.com.ar/hello_world">http://www.ttt.com.ar/...</A>

Pseudocode of what I mean:

 $string = preg_replace("/([\w]+:\/\/[\w-?&;#~=\.\/\@]+[\w\/])/i","<a target=\"_blank\" href=\"$1\">substring($1,0,24)..</A>",$string);

Is this even possible? Probably Im just doing all wrong :)

Thanks in advance.

Answer 1

Check out preg_replace_callback():

$string = 'http://www.ttt.com.ar/hello_world';

$string = preg_replace_callback(
    "/([\w]+:\/\/[\w-?&;#~=\.\/\@]+[\w\/])/i",
    function($matches) {
        $link = $matches[1];
        $substring = substr($link, 0, 24) . '..';
        return "<a target=\"_blank\" href=\"$link\">$substring</a>";
    },
    $string
);

var_dump($string);
// <a target="_blank" href="http://www.ttt.com.ar/hello_world">http://www.ttt.com.ar/...</a>

Note, you can also use the e modifier in PHP to execute functions in your preg_replace(). This has been deprecated in PHP 5.5.0, in favor of preg_replace_callback().

Answer 2

You can use a capturing group inside of a lookahead like this:

preg_replace(
    "/((?=(.{24}))[\w]+:\/\/[\w-?&;#~=\.\/\@]+[\w\/])/i",
    "<a target=\"_blank\" href=\"$1\">$2..</A>",
     $string);

This will capture the entire URL in group 1, but it will also capture the first 24 characters of it in group 2.

Answer 3

You are showing bad practice. Regexes should not being used to parse or modify xml content from application's context.

Suggests:

• Use a DOM parsing to read and modify the value
• use parse_url() to get the protocol + domain name

Example:

$doc = new DOMDocument();
$doc->loadHTML(
    '<a target="_blank" href="http://www.ttt.com.ar/hello_world">http://www.ttt.com.ar/hello_world</A>'#
);

$link = $doc->getElementsByTagName('a')->item(0);
$url = parse_url($link->nodeValue);

$link->nodeValue = $url['scheme'] . '://' . $url['host'] . '/...';

echo $doc->saveHTML();