Makefile

A makefile consists of a set of rules. A rule consists of 3 parts: a target, a list of pre-requisites and a command, as follows:
target: pre-req-1 pre-req-2 …
command

Simple Makefile

the makefile can be named “makefile”, “Makefile” or “GNUMakefile”, without file extension

all: hello.exe

hello.exe: hello.o
	 gcc hello.o -o hello.exe

hello.o: hello.c
	 gcc -c hello.c
     
clean:
	 rm hello.o hello.exe

this makefile builds hello.c into hello.exe

• In the above example, the rule “all” has a pre-requisite “hello.exe”. make cannot find the file “hello.exe”, so it looks for a rule to create it. The rule “hello.exe” has a pre-requisite “hello.o”. Again, it does not exist, so make looks for a rule to create it. The rule “hello.o” has a pre-requisite “hello.c”. make checks that “hello.c” exists and it is newer than the target (which does not exist). It runs the command “gcc -c hello.c”. The rule “hello.exe” then run its command “gcc -o hello.exe hello.o”. Finally, the rule “all” does nothing

// hello.c
#include <stdio.h>
 
int main() {
    printf("Hello, world!\n");
    return 0;
}

Running Makefile

have both makefile and hello.c under the same directory

to build, execute the make command

> ls
hello.c makefile
> make
gcc -c hello.c
gcc -o hello.exe hello.o
> ls
hello.c hello.o hello.exe makefile

to undo build, run the following command

> make clean
hello.c makefile