According to Posix, Make comments start with #
and continue until an unescaped newline is reached.
$ cat Makefile
# A = foo \
bar \
baz
all:
@echo ok
$ make # GNU make
ok
However this is not always the case. Some implementations
discard everything from # through the end of the line, ignoring any
trailing backslash.
$ pmake # BSD make
"Makefile", line 3: Need an operator
Fatal errors encountered -- cannot continue
Therefore, if you want to comment out a multi-line definition, prefix each
line with #, not only the first.
# A = foo \
# bar \
# baz