# We start with a rule to make ‹getenv› again:

getenv: getenv.o
	cc -o getenv getenv.o

# We also add -std=c99 to CFLAGS:

CFLAGS += -std=c99

# Out of the box, ‹make› knows how to compile C sources (‹.c› files)
# into object files (‹.o› files). This time, however, we will tell
# it how to do that anyway. The traditional way to tell ‹make› that
# ‹.c› and ‹.o› are «suffixes» (which are special for ‹make›) is
# this:

.SUFFIXES: .c .o

# If .c and .o are suffixes, we can write special rules (called
# inference rules) which tell ‹make› how to go from «any» ‹.c› file
# to a corresponding ‹.o› file like this:

.c.o:
	cc -c $(CFLAGS) -o $@ $<

# We have used some magic variables there. The $@ is the name of the
# target to make and is defined in any rule. The $< is the name of
# the prerequisite (the .c file in this case) and may or may not be
# available in standard (non-suffix) rules.
#
# Now, since we have the suffix rule, we don't have to tell ‹make›
# how to build ‹getenv.o›. Try running those commands:
#
#     $ rm -f getenv.o getenv
#     $ make -f suffixes.mk

# You can now go on to read ‹autodep.mk›.