- preg_replace: documentation ( source)
<?php
$text ="I found some really good articles on such and such topic. Here are a few links to check out: http://www.example.com/hOSDHOUA and https://www.mywebsite.com/h/yIFeelLowIfImHigh and http://example-site.com/today-is-a-beautiful-day/. ";
$reg_exUrl = "/(http|https|ftp|ftps)\:\/\/[a-zA-Z0-9\-\.]+\.[a-zA-Z]{2,3}(\/\S*)?/";
echo preg_replace($reg_exUrl, "<a href=$0>$0</a> ", $text);