Makefile

Short notes about everything that one might needed in writing Makefile

Command lines

Calling make with makefile other than makefile

$ make -f NewMakeFile

Dry-run

$ make -n

Execute n jobs at once

$ make -j n

Targets and actions

Syntax of a rule

target: dependent1 dependent2
	action1
	action2

First target is the default target.

Calling nested Makefiles

subtarget:
  	cd subdir && $(MAKE)

here, $(MAKE) must be used to ensure all command line arguments are passed on to the nested make

Tell make that some targets are not a file

.PHONY: all clean test install

To ignore errors on an action, prefix with -; to suppress echoing the action command to stdout, prefix with @

clean:
  	-rm file1 file2 file3 file4
  	@echo Clean finished.

Variables

By convention, all variables are in uppercase.

CC = gcc
main: main.c
  ${CC} -o main main.c

There are different way to assign variables:

Simple assignment: Value on RHS is expanded immediately

CC := ${GCC} ${FLAGS}

Recursive assignment: Value on RHS is expanded only when LHS is encountered in action

CC = ${GCC} ${FLAGS}

Conditional assignment: Value is assigned only if the variable does not have a value yet

CC ?= gcc

Appending: Text is appended to an existing variable

CC = gcc
CC += -Wall

Patterns

%.o : %.c
  gcc -c -o $@ $^ | tee $*.log

To obtain command output from shell, use

LS = $(shell ls)