Make and Makefiles

• make is a utility used to build executables from source code by following rules in a makefile.
• Automates the build process.
• Allows one to effeciently compile an executable.
• Reduce compile time by not recompiling source code that has not changed.

The following is known as a rule:
----------
target(s): prerequisite(s) (dependencies) (dependency list)
	command(s) (sometimes called recipes)
----------

target(s): prerequisite(s) (dependencies) (dependency list)
	command_1
	command_2
	command_3
	    .
	    .
	    .
	command_n

target ... : dependency ...
	command
	...
	...
	...

Example:
----------

.PHONY : all clean

all: hello_world

hello_world: hello.cpp hello.h
	g++ hello.cpp -o hello_world

# delete everything execpt source files
clean:
	rm hello_world
	rm *.o

• A makefile consists of one or more Rules. Rules tell when and how to rebuild target(s).
• The targets are sometimes called the goal of the rule.
• make ultimately ensures that the goal(s) of the makefile are up-to-date.
• Phony (Psuedo) Targets - target that does not have a real, corresponding file (file that we want to create).
• all and clean are pseudo targets.
• The pseudo targets will no longer work if a file with the corresponding name really exists. Therefore, pseudo targets should be explicitely stated in the Makefile.
• To explicitely define a Psuedo Target, use the special, built-in target name, .PHONY. (for other special built-in targets, see Special Built-in Target Names).
• To call a phony target, invoke make with the psuedo target name as the argument (e.g. make clean).
• If no argument is specified, the first target (excluding targets starting with a period) will be the default goal.
• If no dependency is listed, then corresponding command(s) for that rule will always be executed.
• To be safe, header files that are included in a given source file should be listed as dependencies in the Makefile.
• GNU make reference
• Automatic variables