Make

Make is a tool which controls the generation of executables and other non-source files of a program from the program's source files.

When a file named Makefile exists in a directory, it can be invoked by running make in the command line.

Makefile

Makefiles are used to help decide which parts of a large program need to be recompiled.[2]

A makefile allows the running of multiple processes in a systematic way, establishing dependency structures and commands needed to complete specific tasks. The makefile is always named Makefile.

An example makefile could be as follows (from [2]):

blah: blah.o
  cc blah.o -o blah # Runs third

blah.o: blah.c
  cc -c blah.c -o blah.o # Runs second

blah.c:
  echo "int main() { return 0; }" > blah.c # Runs first

[This] Makefile has three separate rules. When you run make blah in the terminal, it will build a program called blah in a series of steps:

  • Make is given blah as the target, so it first searches for this target
  • blah requires blah.o, so make searches for the blah.o target
  • blah.o requires blah.c, so make searches for the blah.c target
  • blah.c has no dependencies, so the echo command is run
  • The cc -c command is then run, because all of the blah.o dependencies are finished
  • The top cc command is run, because all the blah dependencies are finished
  • That's it: blah is a compiled c program

Rules

A rule is a target with an optional set of dependencies, and a set of commands to run. The first line of a Makefile is the "default goal"[3], but any specific rules can be specified as arguments following the make invocation.

The target is the destination file to be created or updated when the rule's commands finish running.

The dependencies are a list of files to be checked if they exist before running the rule.

The commands are the commands to be run if the rule is executed.

So from the above example's first rule, blah is the target, blah.o is the single dependency, and the cc line is the only command.

all

The all target will specify all the rules you want to run in place of a single rule.

all: one two three

one:
  # commands
two:
  # commands
three:
  # commands

clean

The clean rule is a standard for cleaning up the directory of compiled executables or whatever[3]. Usually looks something like this:

clean:
  rm blah.o

Assuming this rule is not the default rule and the word clean is not referenced as a dependency in any other rule, this can only be invoked by running make clean.

Variables

Variables are strictly text substitution. Variables will be replaced by their content before they are run. For instance, the following will echo "Hello World!":

WORD = "Hello"

default:
  echo "$(WORD) World!"

Command line arguments can be brought in using a key=value structure, referring to the key within the Makefile as $(key).

Makefile

default:
  gcc -lncurses $(f).c

Command line

$ make f=pomodoro
# gcc -lncurses pomodoro.c
$ make f='timer'
# gcc -lncurses timer.c

References

  1. https://www.gnu.org/software/make/
  2. https://makefiletutorial.com/
  3. http://web.mit.edu/gnu/doc/html/make_2.html

Last modified: 202209081655