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11.3 Using the System Type

How do you use a canonical system type? Usually, you use it in one or more case statements in `configure.ac' to select system-specific C files. Then, using AC_CONFIG_LINKS, link those files which have names based on the system name, to generic names, such as `host.h' or `target.c' (see section 4.10 Creating Configuration Links). The case statement patterns can use shell wild cards to group several cases together, like in this fragment:

case $target in
i386-*-mach* | i386-*-gnu*)
             obj_format=aout emulation=mach bfd_gas=yes ;;
i960-*-bout) obj_format=bout ;;

and later in `configure.ac', use:


Note that the above example uses $target because it's taken from a tool which can be built on some architecture ($build), run on another ($host), but yet handle data for a third architecture ($target). Such tools are usually part of a compiler suite, they generate code for a specific $target.

However $target should be meaningless for most packages. If you want to base a decision on the system where your program will be run, make sure you use the $host variable, as in the following excerpt:

case $host in
  *-*-msdos* | *-*-go32* | *-*-mingw32* | *-*-cygwin* | *-*-windows*)

You can also use the host system type to find cross-compilation tools. See section 5.2.2 Generic Program and File Checks, for information about the AC_CHECK_TOOL macro which does that.

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