6.8 Multiple Cases

Some operations are accomplished in several possible ways, depending on the OS variant. Checking for them essentially requires a “case statement”. Autoconf does not directly provide one; however, it is easy to simulate by using a shell variable to keep track of whether a way to perform the operation has been found yet.

Here is an example that uses the shell variable fstype to keep track of whether the remaining cases need to be checked. Note that since the value of fstype is under our control, we don't have to use the longer ‘test "x$fstype" = xno’.

     AC_MSG_CHECKING([how to get file system type])
     fstype=no
     # The order of these tests is important.
     AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/statvfs.h>
     #include <sys/fstyp.h>]])],
                       [AC_DEFINE([FSTYPE_STATVFS], [1],
                          [Define if statvfs exists.])
                        fstype=SVR4])
     if test $fstype = no; then
       AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/statfs.h>
     #include <sys/fstyp.h>]])],
                       [AC_DEFINE([FSTYPE_USG_STATFS], [1],
                          [Define if USG statfs.])
                        fstype=SVR3])
     fi
     if test $fstype = no; then
       AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include <sys/statfs.h>
     #include <sys/vmount.h>]])]),
                       [AC_DEFINE([FSTYPE_AIX_STATFS], [1],
                          [Define if AIX statfs.])
                        fstype=AIX])
     fi
     # (more cases omitted here)
     AC_MSG_RESULT([$fstype])