PHP: Properly convert addresses to clickeable links in string - php

Question

I need to automatically parse a string and find if a link to my site is present, automatically replace the address by a clickeable HTML link.
Supposing my site adresses are www.mysite.com + wap.mysite.com + m.mysite.com, I need to convert:
My pictures at m.mysite.com/user/id are great.
to:
My pictures at mysite.com/user/id are great.
The question is how to do this (with ereg_replace?) instead of using tons of lines of code.
Notice that the result must be a relative URL, so that the current protocol and subdomain is used for the target link. If the user is in the m subdomain of the HTTPS version, the target will be the m subdomain of the HTTPS protocol and so on. Only links to mysite.com must be linked, any other links must be treated as ordinary plain text. Thanks in advance!

Answer 1

First piece of advice, stay away from ereg, it's been deprecated for a long time. Second, you can probably google and experiment to concoct a preg expression that works well for you, so tweak what I have here to suit your needs.
I was able to put together a fairly simple regex pattern to search for the URLs.
preg_match("/m.mysite.com\S+/", $str, $matches);
Once you have the URLs, I'd suggest parse_url instead of regex.
And here is the code
$sSampleInput = 'My pictures at http://m.mysite.com/user/id are great.';
// Search for URLs but don't look for the scheme, we'll add that later
preg_match("/m.mysite.com\S+/", $sSampleInput, $aMatches);
$aResults = array();
foreach($aMatches as $sUrl) {
// Tack a scheme afront the URL
$sUrl = 'http://' . $sUrl;
// Try validating the URL, requiring host & path
if(!filter_var(
$sUrl,
FILTER_VALIDATE_URL,
FILTER_FLAG_HOST_REQUIRED|FILTER_FLAG_PATH_REQUIRED)) {
trigger_error('Invalid URL: ' . $sUrl . PHP_EOL);
continue;
} else
$aResults[] =
'<a href="' . parse_url($sUrl, PHP_URL_PATH) .
'" target="_blank">' . $sUrl . '</a>';
}