(automake-1.16.info)Subdirectories

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7.1 Recursing subdirectories
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In packages using make recursion, the top level ‘Makefile.am’ must tell
Automake which subdirectories are to be built.  This is done via the
‘SUBDIRS’ variable.

   The ‘SUBDIRS’ variable holds a list of subdirectories in which
building of various sorts can occur.  The rules for many targets (e.g.,
‘all’) in the generated ‘Makefile’ will run commands both locally and in
all specified subdirectories.  Note that the directories listed in
‘SUBDIRS’ are not required to contain ‘Makefile.am’s; only ‘Makefile’s
(after configuration).  This allows inclusion of libraries from packages
that do not use Automake (such as ‘gettext’; see also Note: Third-Party
Makefiles).

   In packages that use subdirectories, the top-level ‘Makefile.am’ is
often very short.  For instance, here is the ‘Makefile.am’ from the GNU
Hello distribution:

     EXTRA_DIST = BUGS ChangeLog.O README-alpha
     SUBDIRS = doc intl po src tests

   When Automake invokes ‘make’ in a subdirectory, it uses the value of
the ‘MAKE’ variable.  It passes the value of the variable ‘AM_MAKEFLAGS’
to the ‘make’ invocation; this can be set in ‘Makefile.am’ if there are
flags you must always pass to ‘make’.

   The directories mentioned in ‘SUBDIRS’ are usually direct children of
the current directory, each subdirectory containing its own
‘Makefile.am’ with a ‘SUBDIRS’ pointing to deeper subdirectories.
Automake can be used to construct packages of arbitrary depth this way.

   By default, Automake generates ‘Makefiles’ that work depth-first in
postfix order: the subdirectories are built before the current
directory.  However, it is possible to change this ordering.  You can do
this by putting ‘.’ into ‘SUBDIRS’.  For instance, putting ‘.’ first
will cause a prefix ordering of directories.

   Using

     SUBDIRS = lib src . test

will cause ‘lib/’ to be built before ‘src/’, then the current directory
will be built, finally the ‘test/’ directory will be built.  It is
customary to arrange test directories to be built after everything else
since they are meant to test what has been constructed.

   In addition to the built-in recursive targets defined by Automake
(‘all’, ‘check’, etc.), the developer can also define his own recursive
targets.  That is done by passing the names of such targets as arguments
to the m4 macro ‘AM_EXTRA_RECURSIVE_TARGETS’ in ‘configure.ac’.
Automake generates rules to handle the recursion for such targets; and
the developer can define real actions for them by defining corresponding
‘-local’ targets.

     % cat configure.ac
     AC_INIT([pkg-name], [1.0]
     AM_INIT_AUTOMAKE
     AM_EXTRA_RECURSIVE_TARGETS([foo])
     AC_CONFIG_FILES([Makefile sub/Makefile sub/src/Makefile])
     AC_OUTPUT
     % cat Makefile.am
     SUBDIRS = sub
     foo-local:
             @echo This will be run by "make foo".
     % cat sub/Makefile.am
     SUBDIRS = src
     % cat sub/src/Makefile.am
     foo-local:
             @echo This too will be run by a "make foo" issued either in
             @echo the 'sub/src/' directory, the 'sub/' directory, or the
             @echo top-level directory.