VPATH: Search Path for All Prerequisites
The value of the make variable VPATH specifies a list of
directories that make should search. Most often, the
directories are expected to contain prerequisite files that are not in the
current directory; however, make uses VPATH as a search
list for both prerequisites and targets of rules.
Thus, if a file that is listed as a target or prerequisite does not exist
in the current directory, make searches the directories listed in
VPATH for a file with that name. If a file is found in one of
them, that file may become the prerequisite (see below). Rules may then
specify the names of files in the prerequisite list as if they all
existed in the current directory. See Writing Shell Commands with Directory Search.
In the VPATH variable, directory names are separated by colons or
blanks. The order in which directories are listed is the order followed
by make in its search. (On MS-DOS and MS-Windows, semi-colons
are used as separators of directory names in VPATH, since the
colon can be used in the pathname itself, after the drive letter.)
For example,
VPATH = src:../headers
specifies a path containing two directories, src and
../headers, which make searches in that order.
With this value of VPATH, the following rule,
foo.o : foo.c
is interpreted as if it were written like this:
foo.o : src/foo.c
assuming the file foo.c does not exist in the current directory but is found in the directory src.