# GNUInstallDirs

Define GNU standard installation directories

Provides install directory variables as defined by the GNU Coding Standards.

## Result Variables

Inclusion of this module defines the following variables:

`CMAKE_INSTALL_<dir>`

> Destination for files of a given type. This value may be passed to the `DESTINATION` options of `install()` commands for the corresponding file type.

`CMAKE_INSTALL_FULL_<dir>`

> The absolute path generated from the corresponding `CMAKE_INSTALL_<dir>` value. If the value is not already an absolute path, an absolute path is constructed typically by prepending the value of the `CMAKE_INSTALL_PREFIX` variable. However, there are some special cases as documented below.

where `<dir>` is one of:

`BINDIR`
  user executables (`bin`)
`SBINDIR`
  system admin executables (`sbin`)
`LIBEXECDIR`
  program executables (`libexec`)
`SYSCONFDIR`
  read-only single-machine data (`etc`)
`SHAREDSTATEDIR`
  modifiable architecture-independent data (`com`)
`LOCALSTATEDIR`
  modifiable single-machine data (`var`)
`LIBDIR`
  object code libraries (`lib` or `lib64` or `lib/<multiarch-tuple>` on Debian)
`INCLUDEDIR`
  C header files (`include`)
`OLDINCLUDEDIR`
  C header files for non-gcc (`/usr/include`)
`DATAROOTDIR`
  read-only architecture-independent data root (`share`)
`DATADIR`
  read-only architecture-independent data (`DATAROOTDIR`)
`INFODIR`
  info documentation (`DATAROOTDIR/info`)
`LOCALEDIR`
  locale-dependent data (`DATAROOTDIR/locale`)
`MANDIR`
  man documentation (`DATAROOTDIR/man`)
`DOCDIR`
  documentation root (`DATAROOTDIR/doc/PROJECT_NAME`)

If the includer does not define a value the above-shown default will be used and the value will appear in the cache for editing by the user.

## Special Cases

The following values of `CMAKE_INSTALL_PREFIX` are special:

`/`

> For `<dir>` other than the `SYSCONFDIR` and `LOCALSTATEDIR`, the value of `CMAKE_INSTALL_<dir>` is prefixed with `usr/` if it is not user-specified as an absolute path. For example, the `INCLUDEDIR` value `include` becomes `usr/include`. This is required by the GNU Coding Standards, which state:

> > When building the complete GNU system, the prefix will be empty and `/usr` will be a symbolic link to `/`.

`/usr`

> For `<dir>` equal to `SYSCONFDIR` or `LOCALSTATEDIR`, the `CMAKE_INSTALL_FULL_<dir>` is computed by prepending just `/` to the value of `CMAKE_INSTALL_<dir>` if it is not user-specified as an absolute path. For example, the `SYSCONFDIR` value `etc` becomes `/etc`. This is required by the GNU Coding Standards.

`/opt/...`

> For `<dir>` equal to `SYSCONFDIR` or `LOCALSTATEDIR`, the `CMAKE_INSTALL_FULL_<dir>` is computed by appending the prefix to the value of `CMAKE_INSTALL_<dir>` if it is not user-specified as an absolute path. For example, the `SYSCONFDIR` value `etc` becomes `/etc/opt/...`. This is defined by the Filesystem Hierarchy Standard.

## Macros

`GNUInstallDirs_get_absolute_install_dir`

      GNUInstallDirs_get_absolute_install_dir(absvar var)

  Set the given variable `absvar` to the absolute path contained within the variable `var`. This is to allow the computation of an absolute path, accounting for all the special cases documented above. While this macro is used to compute the various `CMAKE_INSTALL_FULL_<dir>` variables, it is exposed publicly to allow users who create additional path variables to also compute absolute paths where necessary, using the same logic.