php regex preg_match on a variable containing a url - php

Question

I'm trying to run a regex on a url to extract all the segments after the host. I can't get it working when the host segment is in a variable and i'm not sure how to get it working
// this works
if(preg_match("/^http\:\/\/myhost(\/[a-z0-9A-Z-_\/.]*)$/", $url, $matches)) {
return $matches[2];
}
// this doesn't work
$siteUrl = "http://myhost";
if(preg_match("/^$siteUrl(\/[a-z0-9A-Z-_\/.]*)$/", $url, $matches)) {
return $matches[2];
}
// this doesn't work
$siteUrl = preg_quote("http://myhost");
if(preg_match("/^$siteUrl(\/[a-z0-9A-Z-_\/.]*)$/", $url, $matches)) {
return $matches[2];
}

Answer 1

In PHP, there is a function called parse_url. (Something similar to what you are trying to achieve through your code).
<?php
$url = 'http://username:password#hostname/path?arg=value#anchor';
print_r(parse_url($url));
echo parse_url($url, PHP_URL_PATH);
?>
OUTPUT :
Array
(
[scheme] => http
[host] => hostname
[user] => username
[pass] => password
[path] => /path
[query] => arg=value
[fragment] => anchor
)
/path

Answer 2

You forgot to escape the / in your variable declaration. One quick fix is to change your regex delimiter from / to #. Try:
$siteUrl = "http://myhost";
if(preg_match("#^$siteUrl(\/[a-z0-9A-Z-_\/.]*)$#", $url, $matches)) { //note the hashtags!
return $matches[2];
}
Or without changing the regex delimiter:
$siteUrl = "http:\/\/myhost"; //note how we escaped the slashes
if(preg_match("/^$siteUrl(\/[a-z0-9A-Z-_\/.]*)$/", $url, $matches)) { //note the hashtags!
return $matches[2];
}