CODEWITHSUNDEEP
bashmakefileconditional-compilation
m.seliverstov
m.seliverstov

Reputation: 305

Ifdef conditional unexpected behavior

I have a Makefile with command like this:

#Makefile
    hello:
        echo 'hello'
        echo $(TAG)
        ifdef TAG
              $(warning MYWARNING)
        else
              $(error MYERROR)
        endif

I use it like:

# make TAG='1.0' hello

I expect that command performs echo 'hello', then echo $(TAG) and $(warning MYWARNING) but I get:

Makefile:17: MYWARNING
Makefile:19: *** MYERROR.  Stop.

What is wrong?

Upvotes: 5

Views: 2911

Answers (1)

Beta
Beta

Reputation: 99084

Let's try some simpler cases(*).

hello:
    echo hello
    $(error MYERROR)

This produces:

Makefile:3: *** MYERROR.  Stop.

Notice that the error blocks the echo, even thought it comes afterward.

Now let's try something silly:

hello:
    ifdef TAG

The result is:

ifdef TAG
make: ifdef: No such file or directory

"ifdef TAG", interpreted as a shell command, makes no sense. And it is interpreted as a shell command because it's in a recipe and preceded by a TAB.

Now let's combine them:

hello:
    ifdef TAG
    $(error MYERROR)

The result is Makefile:3: *** MYERROR. Stop. So the error obscures the fact that the ifdef... was incorrect.

Do we want a shell conditional, or a Make conditional? If we want to Make to act on it (with error or warning), then it must be a Make conditional, so we must not preceded it with a TAB:

hello:
ifdef TAG
    $(warning MYWARNING)
else
    $(error MYERROR)
endif

This works as intended.

(*) as you ought to have tried before you posted.

Upvotes: 6

Related Questions