I'm new to building Makefiles and am trying to determine how fail a build target if a variable is empty. I want to be able to pass in the variable as an environment variable or as a make parameter.
Say I have a makefile like this:
VER ?=
step0:
echo "step0 should work"
step1:
echo "step1 should enforce variable"
ifeq($(VER), "")
$(error VER is not set)
endif
echo "Success: Value of Ver ${VER}"
step2:
echo "step2 should work"
I want to be able to run the following test cases:
VER="foo" make step1
# should result in printing the "Success:" line
OR
export VER=foo
make step1
# should result in printing the "Success:" line
OR
make step1 VER=foo
# should result in printing the "Success:" line
OR
make step1
# should result in printing "VER is not set"
However, when I run make step using any of the above, I always get the VER is not set error.
Simply put, how can I test for a variable in a specific make target and respond with an error message if it's not set? (but other make targets would not care if the variable is set or not)
A couple of things:
First, you must keep your Make commands and shell commands neatly segregated. This:
ifeq ($(A),$(B))
...
endif
Is Make syntax. You would probably have trouble if you passed that ifeq (...) to the shell. The commands in a makefile recipe are shell commands, to be passed to the shell. To use the Make ifeq conditional in the middle of a rule, do it like this:
step1:
some command
ifeq ($(A),$(B))
another command
endif
yet another command
Note that there are no TABs preceding ifeq and endif; those are not commands to be passed to the shell, they are for consumption by Make.
Second, this:
ifeq(...)
should be this:
ifeq (...)
The space matters (at least in my version of Make).
Third, this:
ifeq ($(VER), "")
should be this:
ifeq ($(VER),)
unless you actually intend that the variable should contain the string ' ""'.
(You could have discovered those last to yourself, playing with ifeq in isolation; always test new tools in isolation.)
After those changes, the makefile works for me. If it doesn't work for you, let me know and we'll hammer it out.
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