Title: notes on GNU make
Subject: As I start using make more, notes I've accomulated.

do "info make" and search for "Pattern Rule Examples"

# Rule to run m4 to create cpp files
M4 := /usr/bin/m4
%.cpp: %.m4
\t$(M4) < $< > $@

Assignment:
http://www.gnu.org/software/make/manual/make.html#Reading-Makefiles

# Normal setting of a variable - values within it are recursively expanded when the variable is used, not when it's declared
VARIABLE = value
# Setting of a variable with simple expansion of the values inside - values within it are expanded at declaration time.
VARIABLE := value
# Setting of a variable only if it doesn't have a value
VARIABLE ?= value
# Appending the supplied value to the existing value
VARIABLE += value

Automatic Variables
http://www.gnu.org/software/make/manual/html_node/Automatic-Variables.html
# target
$@
# All prerequisits, no repeats
$^
# All prerequisits, repeates
$+
# first prereqisit to be rebuilt
$<
# The target member name, when the target is an archive member. For foo.a(bar.o) ‘$%’ is bar.o. ‘$%’ empty when target is not archive member.
$%
#  The names of all the order-only prerequisites, with spaces between them. 
$|
# The stem with which an implicit rule matches 
$*