带有反斜杠的正则表达式在preg_match_all中不起作用

Question

I am trying to get the subdivision name (which sometimes can contain spaces) however I keep getting an error

Warning: Invalid argument supplied for foreach()

I know my current regex does not support spaces which I also need help with but I think the backslash is whats breaking it in preg_match_all

$line = "WORK ORDERS\Subdivision Subdivision\Sec. 64\72751401_123 street dr.pdf"
$ptn2 = "/\\[a-zA-Z]+\\/";
preg_match_all($ptn2, $line, $matches2, PREG_SET_ORDER);

Answer 1

Added \h to match horizontal spaces.

$ptn2 = '~\\[a-zA-Z\h]+\\~';
preg_match_all($ptn2, $line, $matches2, PREG_SET_ORDER);

DEMO