PHP Substring of a regex replacement - php

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();