12.5 Backslash-Newline in Make Comments

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