$re = '`(?<!\S)(?:(@[^\s@]+)(?!\S)[^h]*(?:h(?!ttp)[^h]*)*+)?\K((?:https?|ftp|file)://\S+)`m';
$str = '@test https://stackoverflow.com/questions/ask
Hello @username you need to check this http://github.com and @username you need to https://stackoverflow.com/questions/ask
This is an email test@test.com http://www.test.test
Hello @username you need to check this htt://github.com and @username you need to
Hello @username check this https://regex101.com/r/D3Imn9/1';
$subst = "";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php