Makefile - Parameters

Makefile

# Don't fear the Makefile
# ...but learn to used it efectively

InMakeVar = "Make var"
FromEnvWithDefault ?= "default from make"

before_var = "something"

all:
	echo "Zmienna zdefiniowana w env vars: $${HOME}"

	# we can provide additional variables to the invocation
	#> `ItsMe=PAWEL make` or `make [target] ItsMe=PaWeL`
	echo "Zmienna $${ItsMe}"

	# use a variable defined in the file
	echo "This was define above: ${InMakeVar}"

	# we can provide default values if not define by env
	# make FromEnvWithDefault="from env"
	echo "Where this comes from: ${FromEnvWithDefault}"

echo:
	# To test invocations with a target
	#> make echo ItsMe=PawLo
	echo "Hello, it's me $${ItsMe} from $${HOME}."

time:
	# and we can exec commands and store results
	# we need '$$' as it works here as env var - also note the ';'
	@now=$$(date +'%Y-%m-%d %H:%M:%S'); \
	echo "Today is nice day $${now}"

# we can provide target specific variable, which even can be calculated
# note: task name needs to be repeated
time2: day_of_week = $$(date +'%A -[%S]')
# We can set another target specific var repeating the form
time2: other_var := "other var"
time2:
	echo "Today is ${day_of_week}, but the other is ${other_var}"

# Note param to 'step-before' is provided here, not just before the task
# also try to change assignment operator to `+=` so it combine both values: `"something" "Is it even possible?"`
step-before: before_var := "Is it even possible?"
cascade: step-before
	# but we don't get value set in `step-before` but the value set above
	echo "Actually variable set in file: ${before_var}"

step-before:
	echo "In before step: ${before_var}"