$re = '/([(\s0-9]+)([lL]\.?)([)\s]+)/';
$str = '2 l.
2l.
2l
cuatro l
lateral
1l.
l.
L.
ls.
Ls.
L
l
(l)
(L)
(ls.)
(Ls.)
(ls)
(Ls)
l.
l.
L
l
3l.
2l.
2l.
4 l.
4l
5L.
lateral
literal
1 litro
1l.
1 l. de agua
1/2 L. de zumo
(l)
1l
l.
';
preg_match_all($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