How to use HAVE_BOOST in ax_boost_base

The ax_boost_base page indicates that it sets HAVE_BOOST. So I tried it in my configure.ac file:

AX_BOOST_BASE([1.48],, [AC_MSG_ERROR([libfoo needs Boost, but it was not found in your system])])
AC_MSG_NOTICE(["HAVE_BOOST value"])
AC_MSG_NOTICE([$HAVE_BOOST])

When I run configure, HAVE_BOOST does not seem to have any value:

checking for boostlib >= 1.48 (104800)... yes
configure: "HAVE_BOOST value"
configure:

How do I use this HAVE_BOOST in my configure.ac? Specifically, I want to append a file into my AC_OUTPUT if HAVE_BOOST is set. For example, if HAVE_BOOST is not set, then I want:

AC_OUTPUT([
Makefile 
include/Makefile
comm/Makefile
ordinary_app/Makefile
])

But if HAVE_BOOST is set, then I want this:

AC_OUTPUT([
Makefile 
include/Makefile
comm/Makefile
ordinary_app/Makefile
boost_enabled_app/Makefile

Solution

You missed to set the result back to some variable. You can try this

AX_BOOST_BASE([1.48],
[have_boost=yes],
[AC_MSG_ERROR([libfoo needs Boost, but it was not found in your system])]
)
AC_MSG_NOTICE(["have_boost value"])
AC_MSG_NOTICE([$have_boost])

The HAVE_BOOST is set in the m4 macro ax_boost_base uses AC_DEFINE that would be generated in config.h. It's not a shell variable. Eventually you can use the var $have_boost to get what you want

if test "$have_boost" != yes; then
    AC_OUTPUT([
    Makefile 
    include/Makefile
    comm/Makefile
    ordinary_app/Makefile
    ])
else
    AC_OUTPUT([
    Makefile 
    include/Makefile
    comm/Makefile
    ordinary_app/Makefile
    boost_enabled_app/Makefile
    ])
fi