|  7.6 Multiple directories 
So far, we've only dealt with single-directory projects.  Automake can
also handle projects with many directories.  The variable `SUBDIRS'
is used to list the subdirectories which should be built.  Here is an
example from Automake itself:
 
 
Automake does not need to know the list of subdirectories statically, so
there is no `EXTRA_SUBDIRS' variable.  You might think that
Automake would use `SUBDIRS' to see which `Makefile.am's to
scan, but it actually gets this information from `configure.in'.
This means that, if you have a subdirectory which is optionally built,
you should still list it unconditionally in your call to
AC_OUTPUTand then arrange for it to be substituted (or not, as
appropriate) atconfiguretime. 
Subdirectories are always built in the order they appear, but cleaning
rules (e.g., maintainer-clean) are always run in the reverse
order.  The reason for this odd reversal is that it is wrong to remove a
file before removing all the files which depend on it. 
You can put `.' into `SUBDIRS' to control when the objects in
the current directory are built, relative to the objects in the
subdirectories.  In the example above, targets in `.' will be built
before subdirectories are built.  If `.' does not appear in
`SUBDIRS', it is built following all the subdirectories.
 
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