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5.7 Recursive Use of 'make'
===========================

Recursive use of 'make' means using 'make' as a command in a makefile.
This technique is useful when you want separate makefiles for various
subsystems that compose a larger system.  For example, suppose you have
a sub-directory 'subdir' which has its own makefile, and you would like
the containing directory's makefile to run 'make' on the sub-directory.
You can do it by writing this:

     subsystem:
             cd subdir && $(MAKE)

or, equivalently, this (*note Summary of Options: Options Summary.):

     subsystem:
             $(MAKE) -C subdir

   You can write recursive 'make' commands just by copying this example,
but there are many things to know about how they work and why, and about
how the sub-'make' relates to the top-level 'make'.  You may also find
it useful to declare targets that invoke recursive 'make' commands as
'.PHONY' (for more discussion on when this is useful, see *note Phony
Targets::).

   For your convenience, when GNU 'make' starts (after it has processed
any '-C' options) it sets the variable 'CURDIR' to the pathname of the
current working directory.  This value is never touched by 'make' again:
in particular note that if you include files from other directories the
value of 'CURDIR' does not change.  The value has the same precedence it
would have if it were set in the makefile (by default, an environment
variable 'CURDIR' will not override this value).  Note that setting this
variable has no impact on the operation of 'make' (it does not cause
'make' to change its working directory, for example).

* Menu:

* MAKE Variable::               The special effects of using '$(MAKE)'.
* Variables/Recursion::         How to communicate variables to a sub-'make'.
* Options/Recursion::           How to communicate options to a sub-'make'.
* -w Option::                   How the '-w' or '--print-directory' option
                                  helps debug use of recursive 'make' commands.