To use NUT libraries in your program, use the following code in your configure (.in or .ac) script:

AC_MSG_CHECKING(for NUT client library (libupsclient))
pkg-config --exists libupsclient --silence-errors
if test $? -eq 0
then
        AC_MSG_RESULT(found (using pkg-config))
        LDFLAGS="$LDFLAGS `pkg-config --libs libupsclient`"
        NUT_HEADER="`pkg-config --cflags libupsclient`"
else
        libupsclient-config --version
        if test $? -eq 0
        then
                AC_MSG_RESULT(found (using libupsclient-config))
                LDFLAGS="$LDFLAGS `libupsclient-config --libs`"
                NUT_HEADER="`libupsclient-config --cflags`"
        else
                AC_MSG_ERROR("libupsclient not found")
        fi
fi

This code will test for pkgconfig support for NUT client library, and fall back to libupsclient-config if not available. It will issue an error if none is found!

The same is also valid for other NUT libraries, such as libnutscan. Simply replace libupsclient occurences in the above example, by the name of the desired library (for example, libnutscan).