Learn X in Y minutes

# Comments can be written like this.

# File should be named Makefile and then can be run as `make <target>`.
# Otherwise we use `make -f "filename" <target>`.

# Warning - only use TABS to indent in Makefiles, never spaces!

#-----------------------------------------------------------------------
# Basics
#-----------------------------------------------------------------------

# Rules are of the format
# target: <prerequisite>
# where prerequisites are optional.

# A rule - this rule will only run if file0.txt doesn't exist.
file0.txt:
    echo "foo" > file0.txt
    # Even comments in these 'recipe' sections get passed to the shell.
    # Try `make file0.txt` or simply `make` - first rule is the default.

# This rule will only run if file0.txt is newer than file1.txt.
file1.txt: file0.txt
    cat file0.txt > file1.txt
    # use the same quoting rules as in the shell.
    @cat file0.txt >> file1.txt
    # @ stops the command from being echoed to stdout.
    -@echo 'hello'
    # - means that make will keep going in the case of an error.
    # Try `make file1.txt` on the commandline.

# A rule can have multiple targets and multiple prerequisites
file2.txt file3.txt: file0.txt file1.txt
    touch file2.txt
    touch file3.txt

# Make will complain about multiple recipes for the same rule. Empty
# recipes don't count though and can be used to add new dependencies.

#-----------------------------------------------------------------------
# Phony Targets
#-----------------------------------------------------------------------

# A phony target. Any target that isn't a file.
# It will never be up to date so make will always try to run it.
all: maker process

# We can declare things out of order.
maker:
    touch ex0.txt ex1.txt

# Can avoid phony rules breaking when a real file has the same name by
.PHONY: all maker process
# This is a special target. There are several others.

# A rule with a dependency on a phony target will always run
ex0.txt ex1.txt: maker

# Common phony targets are: all make clean install ...

#-----------------------------------------------------------------------
# Automatic Variables & Wildcards
#-----------------------------------------------------------------------

process: file*.txt  #using a wildcard to match filenames
    @echo $^    # $^ is a variable containing the list of prerequisites
    @echo $@    # prints the target name
    #(for multiple target rules, $@ is whichever caused the rule to run)
    @echo $<    # the first prerequisite listed
    @echo $?    # only the dependencies that are out of date
    @echo $+    # all dependencies including duplicates (unlike normal)
    #@echo $|   # all of the 'order only' prerequisites

# Even if we split up the rule dependency definitions, $^ will find them
process: ex1.txt file0.txt
# ex1.txt will be found but file0.txt will be deduplicated.

#-----------------------------------------------------------------------
# Patterns
#-----------------------------------------------------------------------

# Can teach make how to convert certain files into other files.

%.png: %.svg
    inkscape --export-png $^

# Pattern rules will only do anything if make decides to create the
# target.

# Directory paths are normally ignored when matching pattern rules. But
# make will try to use the most appropriate rule available.
small/%.png: %.svg
    inkscape --export-png --export-dpi 30 $^

# make will use the last version for a pattern rule that it finds.
%.png: %.svg
    @echo this rule is chosen

# However make will use the first pattern rule that can make the target
%.png: %.ps
    @echo this rule is not chosen if *.svg and *.ps are both present

# make already has some pattern rules built-in. For instance, it knows
# how to turn *.c files into *.o files.

# Older makefiles might use suffix rules instead of pattern rules
.png.ps:
    @echo this rule is similar to a pattern rule.

# Tell make about the suffix rule
.SUFFIXES: .png

#-----------------------------------------------------------------------
# Variables
#-----------------------------------------------------------------------
# aka. macros

# Variables are basically all string types

name = Ted
name2="Sarah"

echo:
    @echo $(name)
    @echo ${name2}
    @echo $name    # This won't work, treated as $(n)ame.
    @echo $(name3) # Unknown variables are treated as empty strings.

# There are 4 places to set variables.
# In order of priority from highest to lowest:
# 1: commandline arguments
# 2: Makefile
# 3: shell environment variables - make imports these automatically.
# 4: make has some predefined variables

name4 ?= Jean
# Only set the variable if environment variable is not already defined.

override name5 = David
# Stops commandline arguments from changing this variable.

name4 +=grey
# Append values to variable (includes a space).

# Pattern-specific variable values (GNU extension).
echo: name2 = Sara # True within the matching rule
    # and also within its remade recursive dependencies
    # (except it can break when your graph gets too complicated!)

# Some variables defined automatically by make.
echo_inbuilt:
    echo $(CC)
    echo ${CXX}
    echo $(FC)
    echo ${CFLAGS}
    echo $(CPPFLAGS)
    echo ${CXXFLAGS}
    echo $(LDFLAGS)
    echo ${LDLIBS}

#-----------------------------------------------------------------------
# Variables 2
#-----------------------------------------------------------------------

# The first type of variables are evaluated each time they are used.
# This can be expensive, so a second type of variable exists which is
# only evaluated once. (This is a GNU make extension)

var := hello
var2 ::= $(var) hello
#:= and ::= are equivalent.

# These variables are evaluated procedurally (in the order that they
# appear), thus breaking with the rest of the language !

# This doesn't work
var3 ::= $(var4) and good luck
var4 ::= good night

#-----------------------------------------------------------------------
# Functions
#-----------------------------------------------------------------------

# make has lots of functions available.

sourcefiles = $(wildcard *.c */*.c)
objectfiles = $(patsubst %.c,%.o,$(sourcefiles))

# Format is $(func arg0,arg1,arg2...)

# Some examples
ls: * src/*
    @echo $(filter %.txt, $^)
    @echo $(notdir $^)
    @echo $(join $(dir $^),$(notdir $^))

#-----------------------------------------------------------------------
# Directives
#-----------------------------------------------------------------------

# Include other makefiles, useful for platform specific code
include foo.mk

sport = tennis
# Conditional compilation
report:
ifeq ($(sport),tennis)
    @echo 'game, set, match'
else
    @echo "They think it's all over; it is now"
endif

# There are also ifneq, ifdef, ifndef

foo = true

ifdef $(foo)
bar = 'hello'
endif