Makefile by Example

Source: Makefile Tutorial By Example

Getting Started

• Makefiles exist to decide whick parts of a large program need to be recompiled
• Alternatives exist like CMake, Bazel and in Java: Ant, Maven, and Gradle, and in other languages specific tools.
• Not required for interpreted languages like Python

files := file1 file2
varx := dude
thing_wrong := *.o # Don't do this! '*' will not get expanded
thing_right := $(wildcard *.o)

targets: prerequisites
    command
    command
    command
    # Reference variabe varx
    echo ${varx}
    echo $(varx)

blah: blah.o
    # compile a file
    cc blah.c -o blah

file1:
    touch file1

clean:
    rm -f blah file1

• Make executes the commands
  • Make decides if it should run the blah target. It will only run if blah doesn’t exist, or blah.c is newer than blah
  • Uses file system timestamps
• make clean is often used as a target that removes the output for other targets. It is a convention but not a special word in make.
• Variables can only be strings
  • Reference using ${} and $() like example above
• Single or double quotes have no meaning to Make

Targets

• all target is a convention to run all targets. It will run by default if make is called without target
• $@ is an automatic variable that contains the current target’s name

Automatic Variables and Wildcards

• * and % are wildcards in Make
  • * searches the filesystem for matching filenames
    • Good practice is wrap * in a wildcard function as thing_right ... $(wildcard *.o)
  • % can be used as:
    • “matching” mode to match one or more characters in a string. This match is called a stem.
    • “replacing” mode, it takes a stem that was matched and replaces that in a string
    • Often used to define rules and in functions

Other Automatic Variables

hey: one two
        # Outputs "hey", since this is the target name
        echo $@

        # Outputs all prerequisites newer than the target
        echo $?

        # Outputs all prerequisites
        echo $^

        touch hey

one:
        touch one

two:
        touch two

Fancy Rules