File: make.info,  Node: Search Algorithm,  Next: Recipes/Search,  Prev: Selective Search,  Up: Directory Search

4.5.3 How Directory Searches are Performed
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When a prerequisite is found through directory search, regardless of
type (general or selective), the pathname located may not be the one
that 'make' actually provides you in the prerequisite list.  Sometimes
the path discovered through directory search is thrown away.

   The algorithm 'make' uses to decide whether to keep or abandon a path
found via directory search is as follows:

  1. If a target file does not exist at the path specified in the
     makefile, directory search is performed.

  2. If the directory search is successful, that path is kept and this
     file is tentatively stored as the target.

  3. All prerequisites of this target are examined using this same
     method.

  4. After processing the prerequisites, the target may or may not need
     to be rebuilt:

       a. If the target does _not_ need to be rebuilt, the path to the
          file found during directory search is used for any
          prerequisite lists which contain this target.  In short, if
          'make' doesn't need to rebuild the target then you use the
          path found via directory search.

       b. If the target _does_ need to be rebuilt (is out-of-date), the
          pathname found during directory search is _thrown away_, and
          the target is rebuilt using the file name specified in the
          makefile.  In short, if 'make' must rebuild, then the target
          is rebuilt locally, not in the directory found via directory
          search.

   This algorithm may seem complex, but in practice it is quite often
exactly what you want.

   Other versions of 'make' use a simpler algorithm: if the file does
not exist, and it is found via directory search, then that pathname is
always used whether or not the target needs to be built.  Thus, if the
target is rebuilt it is created at the pathname discovered during
directory search.

   If, in fact, this is the behavior you want for some or all of your
directories, you can use the 'GPATH' variable to indicate this to
'make'.

   'GPATH' has the same syntax and format as 'VPATH' (that is, a space-
or colon-delimited list of pathnames).  If an out-of-date target is
found by directory search in a directory that also appears in 'GPATH',
then that pathname is not thrown away.  The target is rebuilt using the
expanded path.