Here is a straightforward makefile that describes the way an
executable file called
edit depends on eight object files
which, in turn, depend on eight C source and three header files.
In this example, all the C files include defs.h, but only those defining editing commands include command.h, and only low level files that change the editor buffer include buffer.h.
edit : main.o kbd.o command.o display.o \ insert.o search.o files.o utils.o cc -o edit main.o kbd.o command.o display.o \ insert.o search.o files.o utils.o main.o : main.c defs.h cc -c main.c kbd.o : kbd.c defs.h command.h cc -c kbd.c command.o : command.c defs.h command.h cc -c command.c display.o : display.c defs.h buffer.h cc -c display.c insert.o : insert.c defs.h buffer.h cc -c insert.c search.o : search.c defs.h buffer.h cc -c search.c files.o : files.c defs.h buffer.h command.h cc -c files.c utils.o : utils.c defs.h cc -c utils.c clean : rm edit main.o kbd.o command.o display.o \ insert.o search.o files.o utils.o
We split each long line into two lines using backslash-newline; this is like using one long line, but is easier to read. To use this makefile to create the executable file called edit, type:
To use this makefile to delete the executable file and all the object files from the directory, type:
In the example makefile, the targets include the executable file ‘edit’, and the object files ‘main.o’ and ‘kbd.o’. The prerequisites are files such as ‘main.c’ and ‘defs.h’. In fact, each ‘.o’ file is both a target and a prerequisite. Commands include ‘cc -c main.c’ and ‘cc -c kbd.c’.
When a target is a file, it needs to be recompiled or relinked if any of its prerequisites change. In addition, any prerequisites that are themselves automatically generated should be updated first. In this example, edit depends on each of the eight object files; the object file main.o depends on the source file main.c and on the header file defs.h.
A shell command follows each line that contains a target and
prerequisites. These shell commands say how to update the target file.
A tab character must come at the beginning of every command line to
distinguish command lines from other lines in the makefile. (Bear in
make does not know anything about how the commands
work. It is up to you to supply commands that will update the target
file properly. All
make does is execute the commands in the rule
you have specified when the target file needs to be updated.)
The target ‘clean’ is not a file, but merely the name of an
action. Since you
do not want to carry out the actions in this rule, ‘clean’ is not a prerequisite of any other rule.
make never does anything with it unless you tell
it specifically. Note that this rule not only is not a prerequisite, it
also does not have any prerequisites, so the only purpose of the rule
is to run the specified commands. Targets that do not refer to files
but are just actions are called phony targets. See Phony Targets, for information about this kind of target. See Errors in Commands, to see how to cause
make to ignore errors
rm or any other command.