CL-USER> (defvar *multiline* "abc
def
ghi")
*MULTILINE*

CL-USER> (with-input-from-string (stream *multiline*)
           (list (read-line stream)
                 (read-line stream)
                 (read-line stream)))
("abc" "def" "ghi")

CL-USER> (with-input-from-string (stream *multiline*)
           (loop for line = (read-line stream nil)
                 while line
                 collect line))
("abc" "def" "ghi")