Preg_replace or preg_replace_callback? - php

Question

I have links on some pages that use an old system such as:
<a href='/app/?query=stuff_is_here'>This is a link</a>
They need to be converted to the new system which is like:
<a href='/newapp/?q=stuff+is+here'>This is a link</a>
I can use preg_replace t0 change some of what i need to, but i also need to replace underscores in the query with +'s instead. My current code is:
//$content is the page html
$content = preg_replace('#(href)="http://www.site.com/app/?query=([^:"]*)(?:")#','$1="http://www.site.com/newapp/?q=$2"',$content);
What I want to do is run str_replace on the $2 variable, so I tried using preg_replace_callback, and could never get it to work. What should I do?

Answer 1

You have to pass a valid callback [docs] as second parameter: a function name, an anonymous function, etc.
Here is an example:
function my_replace_callback($match) {
$q = str_replace('_', '+', $match[2]);
return $match[1] . '="http://www.site.com/newapp/?q=' . $q;
}
$content = preg_replace_callback('#(href)="http://www.site.com/app/?query=([^:"]*)(?:")#', 'my_replace_callback', $content);
Or with PHP 5.3:
$content = preg_replace_callback('#(href)="http://www.site.com/app/?query=([^:"]*)(?:")#', function($match) {
$q = str_replace('_', '+', $match[2]);
return $match[1] . '="http://www.site.com/newapp/?q=' . $q;
}, $content);
You may also want to try with a HTML parser instead of a regex: How do you parse and process HTML/XML in PHP?

Answer 2

Parsing your document with dom, searching for all "a" tags and then replacing could be a good way. Someone already commented posting you this link to show you that regex isn't always the best way to work with html.
Ayways this code should work:
<?php
$dom = new DOMDocument;
//html string contains your html
$dom->loadHTML($html);
?><ul><?
foreach( $dom->getElementsByTagName('a') as $node ) {
//look for href attribute
if( $node->hasAttribute( 'href' ) ) {
$href = $node->getAttribute( 'href' );
// change hrefs value
$node->setAttribute( "href", preg_replace( "/\/app\/\?query=(.*)/", "/newapp/?q=\1", $href ) );
}
}
//save new html
$newHTML = $dom->saveHTML();
?>
Notice that i did this with preg_replace but this can be done with str_ireplace or str_replace
$newHref = str_ireplace("/app/?query=", "/newapp/?q=", $href);

Answer 3

Or you can use simply preg_match() and collect matched strings. Then apply str_replace() to one of the matches and replace "+" to "_".
$content = preg_match('#href="\/[^\/]\/\?query=([^:"]+)#', $matches)
$matches[2] = 'newapp';
$matches[4] = str_replace('_', '+', $matches[4]);
$result = implode('', $matches)

Answer 4

Pass arrays to preg_replace as pattern and replacement:
preg_replace(array('|/app/|', '_'), array('/newappp/', '+'), $content);