(autoconf.info)VPATH and Make

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11.13 `VPATH' and Make

Posix does not specify the semantics of `VPATH'.  Typically, `make'
supports `VPATH', but its implementation is not consistent.

   Autoconf and Automake support makefiles whose usages of `VPATH' are
portable to recent-enough popular implementations of `make', but to
keep the resulting makefiles portable, a package's makefile prototypes
must take the following issues into account.  These issues are
complicated and are often poorly understood, and installers who use
`VPATH' should expect to find many bugs in this area.  If you use
`VPATH', the simplest way to avoid these portability bugs is to stick
with GNU `make', since it is the most commonly-used `make' among
Autoconf users.

   Here are some known issues with some `VPATH' implementations.

* VPATH and Double-colon
Problems with `::' on ancient hosts
* $< in Explicit Rules
`$<' does not work in ordinary rules
* Automatic Rule Rewriting
`VPATH' goes wild on Solaris
* Tru64 Directory Magic
`mkdir' goes wild on Tru64
* Make Target Lookup
More details about `VPATH' lookup

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