I needed to do some conditional target-based execution via my makefiles. To make them truly generic, I needed to deduce directory structure that I was sitting in.
One of the things I had to do was to check for existence of a file or directory. Now since Makefiles have a different syntax than ordinary shell, compounded by the problem of interfacing with the *nix shell, it took me some time to figure out/learn how to do this.

The syntax (for GNU make) is

ifeq (exists, $(shell [ -d directory_name ] ) && echo exists )
$(warning hi… I did it)
endif

At first I tried to do

ifeq (1, $(shell [ -d directory_name ] ) )
$(warning hi… I did it)
endif

but this did’nt work, because the shell interface does not return a numeric status (atleast I think so). But in the syntax that works, by the power of logic, the “echo exists” will take place if and only if the “shell” command works.
Ergo, I can check for directories.

whew!!

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