make(1)

Anatomy of `make` rules

target .. : prerequisite ..
	recipe
	..

target: an output generated by the rule
prerequisite: an input that is used to generate the target
recipe: list of actions to generate the output from the input

Use make -p to print all rules and variables (implicitly + explicitly defined).

Pattern rules & Automatic variables

Pattern rules

A pattern rule contains the % char (exactly one of them) and look like this example:

%.o : %.c
	$(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@

The target matches files of the pattern %.o, where % matches any none-empty substring and other character match just them self.

The substring matched by % is called the stem.

% in the prerequisite stands for the matched stem in the target.

Automatic variables

As targets and prerequisites in pattern rules can't be spelled explicitly in the recipe, make provides a set of automatic variables to work with:

$@: Name of the target that triggered the rule.
$<: Name of the first prerequisite.
$^: Names of all prerequisites (without duplicates).
$+: Names of all prerequisites (with duplicates).
$*: Stem of the pattern rule.

# file: Makefile

all: foobar blabla

foo% bla%: aaa bbb bbb
	@echo "@ = $@"
	@echo "< = $<"
	@echo "^ = $^"
	@echo "+ = $+"
	@echo "* = $*"
	@echo "----"

aaa:
bbb:

Running above Makefile gives:

@ = foobar
< = aaa
^ = aaa bbb
+ = aaa bbb bbb
* = bar
----
@ = blabla
< = aaa
^ = aaa bbb
+ = aaa bbb bbb
* = bla
----

Variables related to filesystem paths:

$(CURDIR): Path of current working dir after using make -C path

Useful functions

Substitution references

Substitute strings matching pattern in a list.

in  := a.o l.a c.o
out := $(in:.o=.c)
# => out = a.c l.a c.c

`filter`

Keep strings matching a pattern in a list.

in  := a.a b.b c.c d.d
out := $(filter %.b %.c, $(in))
# => out = b.b c.c

`filter-out`

Remove strings matching a pattern from a list.

in  := a.a b.b c.c d.d
out := $(filter-out %.b %.c, $(in))
# => out = a.a d.d

`abspath`

Resolve each file name as absolute path (don't resolve symlinks).

$(abspath fname1 fname2 ..)

### `realpath`
Resolve each file name as canonical path.
```make
$(realpath fname1 fname2 ..)

Notes