In a makefile, I'd like to define a variable specifying whether the current redhat-release is greater than 5.3. (This variable will be passed to gcc as a #define)
So far I've come up with:
# Find out which version of Red-Hat we're running
RH_VER_NUM = $(shell /bin/grep -o [0-9].[0-9] /etc/redhat-release)
RH_GT_5_3 = $RH_VER_NUM > '5.3'
What would be the correct way to define RH_GT_5_3?
GNU Make doesn't contain any string comparisons other than equality, and test can only do less-than/greater-than tests on integers. Split the version number into its integral parts and do the comparison that way. Try this (note also that := is better than = here, as make's lazy evaluation would call your $(shell) commands many more times than required:
RH_VER_MAJOR := $(shell echo $(RH_VER_NUM) | cut -f1 -d.)
RH_VER_MINOR := $(shell echo $(RH_VER_NUM) | cut -f2 -d.)
RH_GT_5_3 := $(shell [ $(RH_VER_MAJOR) -gt 5 -o \( $(RH_VER_MAJOR) -eq 5 -a $(RH_VER_MINOR) -ge 3 \) ] && echo true)
ifeq ($(RH_GT_5_3),true)
CPPFLAGS += -DRH_GT_5_3=1
endif