If condition inside a target in a Makefile

Question

I want to do something like this, where I want to run a svn commit if a file has changed. The file has a timestamp which always changes. So if anything more than timestamp changes , then I want to commit the file.

The makefile will have something similar to this. But the If condition is not working properly. It is getting executed even when if is not satisfied. Can someone help me out what is the problem in If here.

    UPDATE_STATE_FILE :
        $(eval NO_LINES_CHANGES_IN_STATE = $(shell svn di STATE/build.state --diff-cmd=diff -x --normal | grep "^[<>]" | wc -l))
        @echo $(NO_LINES_CHANGES_IN_STATE)
    ifneq ($(strip $(NO_LINES_CHANGES_IN_STATE)), 2)
    ifneq ($(strip $(NO_LINES_CHANGES_IN_STATE)), 0)
        @echo $(NO_LINES_CHANGES_IN_STATE)
        $(SVN) commit;
        $(SVN) update;
    endif
    endif

Answer 1

You cannot mix make conditionals inside command rules. Make conditionals are like preprocessor statements in C or C++; they are handled as the file is read in, before any processing (like running rules) is performed.

If you want conditionals inside the rules you have to write the rule using shell conditionals, not make conditionals:

UPDATE_STATE_FILE :
        @NO_LINES_CHANGES_IN_STATE=`svn di STATE/build.state --diff-cmd=diff -x --normal | grep "^[<>]" | wc -l`; \
        echo $$NO_LINES_CHANGES_IN_STATE; \
        if [ $$NO_LINES_CHANGES_IN_STATE -ne 2 ] && [ $$NO_LINES_CHANGES_IN_STATE -ne 0 ]; then \
            echo $$NO_LINES_CHANGES_IN_STATE; \
            $(SVN) commit; \
            $(SVN) update; \
        fi

Answer 2

After reading the answer given by @MadScientist, I came up with a different approach.

Not knowing if shell conditionals will work in any environment (windows vs. linux), I wrapped the rules inside the conditional instead of having a conditional inside the rule. i.e.

ifdef MY_FLAG
%.o: %.c
    $(CC) -o $@ -c $^ $(CFLAGS)

else
%.o: %.c
    @$(CC) -o $@ -c $^ $(CFLAGS)

endif

Good luck to anyone visiting here.

EDIT

As pointed out by James Moore in the comments, this different approach requires care and notice as to when and how variables are defined in relation to the placement of the if statement in the control flow.