5.4 Packages with Multiple Outputs

Often, packages defined in Guix have a single output—i.e., the source package leads to exactly one directory in the store. When running guix install glibc, one installs the default output of the GNU libc package; the default output is called out, but its name can be omitted as shown in this command. In this particular case, the default output of glibc contains all the C header files, shared libraries, static libraries, Info documentation, and other supporting files.

Sometimes it is more appropriate to separate the various types of files produced from a single source package into separate outputs. For instance, the GLib C library (used by GTK+ and related packages) installs more than 20 MiB of reference documentation as HTML pages. To save space for users who do not need it, the documentation goes to a separate output, called doc. To install the main GLib output, which contains everything but the documentation, one would run:

guix install glib

The command to install its documentation is:

guix install glib:doc

While the colon syntax works for command-line specification of package outputs, it will not work when using a package variable in Scheme code. For example, to add the documentation of glib to the globally installed packages of an operating-system (see operating-system Reference), a list of two items, the first one being the package variable and the second one the name of the output to select (a string), must be used instead:

(use-modules (gnu packages glib))
;; glib-with-documentation is the Guile symbol for the glib package
(operating-system
 ...
 (packages
  (append
   (list (list glib-with-documentation "doc"))
         %base-packages)))

Some packages install programs with different “dependency footprints”. For instance, the WordNet package installs both command-line tools and graphical user interfaces (GUIs). The former depend solely on the C library, whereas the latter depend on Tcl/Tk and the underlying X libraries. In this case, we leave the command-line tools in the default output, whereas the GUIs are in a separate output. This allows users who do not need the GUIs to save space. The guix size command can help find out about such situations (see Invoking guix size). guix graph can also be helpful (see Invoking guix graph).

There are several such multiple-output packages in the GNU distribution. Other conventional output names include lib for libraries and possibly header files, bin for stand-alone programs, and debug for debugging information (see Installing Debugging Files). The outputs of a package are listed in the third column of the output of guix package --list-available (see Invoking guix package).