(automake-1.16.info)Conditional Subdirectories

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7.2 Conditional Subdirectories
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It is possible to define the ‘SUBDIRS’ variable conditionally if, like
in the case of GNU Inetutils, you want to only build a subset of the
entire package.

   To illustrate how this works, let’s assume we have two directories
‘src/’ and ‘opt/’.  ‘src/’ should always be built, but we want to decide
in ‘configure’ whether ‘opt/’ will be built or not.  (For this example
we will assume that ‘opt/’ should be built when the variable ‘$want_opt’
was set to ‘yes’.)

   Running ‘make’ should thus recurse into ‘src/’ always, and then maybe
in ‘opt/’.

   However ‘make dist’ should always recurse into both ‘src/’ and
‘opt/’.  Because ‘opt/’ should be distributed even if it is not needed
in the current configuration.  This means ‘opt/Makefile’ should be
created _unconditionally_.

   There are two ways to setup a project like this.  You can use
Automake conditionals (Note: Conditionals) or use Autoconf ‘AC_SUBST’
variables (Note: Setting Output Variables.
).  Using Automake conditionals is the preferred solution.
Before we illustrate these two possibilities, let’s introduce
‘DIST_SUBDIRS’.

SUBDIRS vs DIST_SUBDIRS

Two sets of directories

Subdirectories with AM_CONDITIONAL

Specifying conditional subdirectories

Subdirectories with AC_SUBST

Another way for conditional recursion

Unconfigured Subdirectories

Not even creating a ‘Makefile’