Question

I need to build a C program which requires a particular Linux package. I set a variable, PACKAGENOTIFICATION, to a shell command which is supposed to check if the package is installed for Ubuntu and print a notification if not:

PACKAGENOTIFICATION := if cat /etc/issue | grep Ubuntu -c >>/dev/null; then if ! dpkg -l | grep libx11-dev -c >>/dev/null; then echo "<insert notification here>"; fi; fi

[...]

maintarget: dependencies
            $(PACKAGENOTIFICATION)
            other_commands

Unfortunately, while making the dependencies, it runs into the files which need the package, and errors out before executing my PACKAGENOTIFICATION. An alternative formulation is to make a separate target whose only purpose is to run the notification:

maintarget: notify other_dependencies
            commands

notify: 
            $(PACKAGENOTIFICATION)

However, since this phantom dependency always needs to be executed, make never reports that the program is up to date.

What’s the best way to have make always report as up to date, but also execute my notification before it dies?

Thanks!

Answer 1

If your version of Make supports “order-only” prerequisites, this will do it:

# Note the pipe
maintarget: other_dependencies | notify
            commands

# This should be an order-only preq of any target that needs the package
notify: 
            $(PACKAGENOTIFICATION)

If not, there are other approaches.