Makefiles By Example

The basic structure of a Makefile is as follows:

dependency-one:
    command1
    command2

dependency-two:
    command3

end-goal: dependency-one dependency-two
    command4
    command5
    # ...
    commandN

When you invoke make end-goal, the following would happen:

• dependency-one (command1, command2)
• dependency-two (command3)
• end-goal (command4, command5, commandN)

Basic stuff

#

Everything after it is a comment, until the next line break.

:=, = and ?=

These are different ways of setting values to variables.

START_TIME := $(shell date)
CURRENT_TIME = $(shell date)
ENABLED ?= no

$(VAR)

Returns the value of the variable VAR.

VIM_DIR := $(HOME)/.vim

@

Do not echo the command that follows.

ninja:
    @echo ""

NOTE: The @ does not need to be right before the command name; the next example works just fine, as the previous one:

lazy-ninja:
    @       echo ""

If, for some reason, you need to check what command would be executed, just invoke the make with the -n option, like this:

make -n lazy-ninja

%, $* and $@

say-my-name-%:
	@echo Given the target $@, your name is $*!

• $@ to represent the full target name of the current target
• $* returns the text that corresponds to % in the target

Special variables

SHELL

Defines the shell program to interpret each goal. Defaults to /bin/sh

SHELL = /bin/bash

.DEFAULT_GOAL

.DEFAULT_GOAL = my-second-goal

.PHONY:

The definitions that follows it should not be interpreted as files.

.PHONY: release-major release-minor release-patch
release-major:
	$(XYZ) --increment major
release-minor:
	$(XYZ) --increment minor
release-patch:
	$(XYZ) --increment patch

Helper functions

shell

Executes a shell command and return its output.

NOW = $(shell date)

define and call

define print_title
echo -----------------
echo $(1)
echo -----------------
endef

main-menu:
	@$(call print_title,"main menu")

ifndef and error

PIP3 := $(shell command -v pip3 2> /dev/null)
ifndef PIP3
define MSG
PIP3 does not seem to be installed.
To install it, follow the instructions found at this website:

	https://pip.pypa.io/en/stable/installing/

endef
$(error $(MSG))
endif

More examples

• The sample Makefile in this repo;
• This Makefile for my vim setup;
• A Makefile for a Go project.