GNU `make'

Node:Commands/Search, Next:Implicit/Search, Previous:Search Algorithm, Up:Directory Search

#### Writing Shell Commands with Directory Search

When a prerequisite is found in another directory through directory search, this cannot change the commands of the rule; they will execute as written. Therefore, you must write the commands with care so that they will look for the prerequisite in the directory where `make` finds it.

This is done with the automatic variables such as `$^` (see Automatic Variables). For instance, the value of `$^` is a list of all the prerequisites of the rule, including the names of the directories in which they were found, and the value of `$@` is the target. Thus:

         foo.o : foo.c
                 cc -c $(CFLAGS) $^ -o $@

(The variable `CFLAGS` exists so you can specify flags for C compilation by implicit rules; we use it here for consistency so it will affect all C compilations uniformly; see Variables Used by Implicit Rules.)

Often the prerequisites include header files as well, which you do not want to mention in the commands. The automatic variable `$<` is just the first prerequisite:

         VPATH = src:../headers
         foo.o : foo.c defs.h hack.h
                 cc -c $(CFLAGS) $< -o $@