Tags: #make #makefile #args #env #vars
In the following example the value of beep will only be used when there is no existing TF_LOG data anywhere.
TF_LOG ?= "beep"
run:
echo $(TF_LOG)
env | grep -i tf_log
Example run:
$ export TF_LOG=test # set TF_LOG in the parent shell
# make will copy this when spinning up a new shell (when running a makefile target)
$ make run
echo test
test
env | grep -i tf_log
TF_LOG=test # value of 'beep' was overridden by the parent shell environment
$ make run -e TF_LOG=trace
echo trace
trace
env | grep -i tf_log
MAKEFLAGS=e -- TF_LOG=trace
TF_LOG=trace # value of 'beep' AND parent shell environment was overridden by make's -e flag (which sets env var within the child shell process it spins up)
$ make run TF_LOG=trace
echo trace
trace
env | grep -i tf_log
MAKEFLAGS=TF_LOG=trace
TF_LOG=trace # value of 'beep' AND parent shell environment was overridden by passing TF_LOG=trace as a makefile 'argument'.
$ TF_LOG=trace make run
echo trace
trace
env | grep -i tf_log
TF_LOG=trace # value of 'beep' AND parent shell environment was overridden by passing TF_LOG=trace as command scoped environment var.
$ unset TF_LOG # to demonstrate when 'beep' will be used
# as TF_LOG doesn't exist in current shell (so Makefile can't copy it)
# nor do we pass in TF_LOG via -e flag or pre/post make target itself
$ make run
echo "beep"
beep
env | grep -i tf_log
make: *** [run] Error 1