$re = '/^([^\s=]+)\h+=\h+(.*(?:\R(?![^\s=]+\h+=\h+).*)*)$/m';
$str = 'groupid = foo
location = westus
randomkey = fbae3700c34cb06c
resourcename = example4-resourcegroup
tls_private_key = -----BEGIN RSA PRIVATE KEY-----
//stuff
-----END RSA PRIVATE KEY-----
foo = 123
faa = 223';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
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