3 Pattern: single backslash and star: "replace literal star"
8 Pattern: double backslash and star: "replace backslash and everything after it"
16 Pattern: single backslash and b: "replace b"
21 Pattern: double backslash and b: "replace backslash and b"
28 Replace str: _\\_\z_ (as variable $s)
29 Pattern: single backslash and b: "replace b"
31 Unquoted =: a\_\\_\z_c
34 Pattern: double backslash and b: "replace backslash and b"