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Defining Custom Suffix Rules in Makefile

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By itself, make knows already that in order to create a .o file, it must use cc -c on the corresponding .c file. These rules are built into make, and you can take advantage of this to shorten your Makefile. If you just indicate just the .h files in the dependency line of the Makefile that the current target is dependent on, make will know that the corresponding .c file is already required. You don't even need to include the command for the compiler.

This reduces our Makefile further, as shown:
OBJECTS = main.o hello.o factorial.o
hello: $(OBJECTS)
        cc $(OBJECTS) -o hello
hellp.o: functions.h
main.o: functions.h 
factorial.o: functions.h 

Make uses a special target, named .SUFFIXES to allow you to define your own suffixes. For example, the dependency line:
.SUFFIXES: .foo .bar
tells make that you will be using these special suffixes to make your own rules.

Similar to how make already knows how to make a .o file from a .c file, you can define rules in the following manner:
        tr '[A-Z][a-z]' '[N-Z][A-M][n-z][a-m]' < $< > $@
        $(CC) $(CFLAGS) -c $<

The first rule allows you to create a .bar file from a .foo file. (Don't worry about what it does, it basically scrambles the file.) The second rule is the default rule used by make to create a .o file from a .c file.

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