Hi, 

Ok, Mk2 then:

a:=$(shell echo "don't mess up this output"; echo  " $$?")

code:=$(lastword $(a))
output:=$(strip $(patsubst %$(code),%,$(a)))
$(info exit code='$(code)')
$(info output='$(output)')

[tnmurphy@4GBL06592 ~]$ make -f t4.mk
exit code='0'
output='don't mess up this output'
make: * No targets.  Stop.

I think that the $(strip) is a bit of a cheat but it's pretty close to what should be done.  This could probably be done completely properly with another patsubst.

To get the exit code:


a:=$(shell cat fred.txt; echo $$?)
$(info exit=$(a))

make -f t.mk
cat: fred.txt: No such file or directory
exit=1

There's no way $(shell ...) failing can or should cause make to stop.  There are many legitimate reasons why the shell exiting with an error should not cause make to fail, and adding this would be an enormous backward-compatibility break.

For your situation, you can just check to see whether the result of the variable was valid; this will also catch the situation where there's an empty file as well as a non-existent one:

a := $(shell cat version.txt)
ifeq (,$(a))
$(error version.txt does not contain a valid version)
endif

I agree it might be useful to find out the exit code of the last $(shell ...) function invocation, so I'm leaving this open as an enhancement request to create a variable containing the exit code of the last $(shell ...) invocation.