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diff --git a/make.html.markdown b/make.html.markdown new file mode 100644 index 00000000..1cf0d8c7 --- /dev/null +++ b/make.html.markdown @@ -0,0 +1,236 @@ +--- +language: make +contributors: + - ["Robert Steed", "https://github.com/robochat"] +filename: Makefile +--- + +A Makefile defines a graph of rules for creating a target (or targets). +It's purpose is the do the minimum amount of work needed to update a +target to the most recent version of the source. Famously written over a +weekend by Stuart Feldman in 1976, it is still widely used (particularly +on Unix) despite many competitors and criticisms. + +There are many varieties of make in existance, this article assumes that +we are using GNU make which is the standard on Linux. + +```make + +# Comments can be written like this. + +# Files should be named Makefile and then be can run as `make <target>`. +# Otherwise we use `make -f "filename" <target>`. + +# Warning - only use TABS to indent in Makefiles, never spaces! + +#----------------------------------------------------------------------- +# Basics +#----------------------------------------------------------------------- + +# 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: faker 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 %.svg + +# 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 %.svg + +# 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. + +#----------------------------------------------------------------------- +# 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 enviroment variables - make imports these automatically. +# 4: make has some predefined variables + +name4 ?= Jean +# Only set the variable if enviroment 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 it's 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 procedurely (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 +``` + + +### More Resources + +[gnu make documentation](https://www.gnu.org/software/make/manual/) +[software carpentry tutorial](http://swcarpentry.github.io/make-novice/) +learn C the hard way [ex2](http://c.learncodethehardway.org/book/ex2.html) [ex28](http://c.learncodethehardway.org/book/ex28.html) + |