Managing Use flags - YoloSoftDE/gentoo-overlay GitHub Wiki
Use-flags are mandatory for almost every ebuild you will ever write. It makes the resulting package flexible to the users needs.
Adding Use-flags to your ebuild
Use-flags are added using the IUSE-variable.
IUSE="debug doc"
Use-flags with a prepeding + are enabled by default. Use-flags with a prepeding - are disabled by default.
IUSE="gnome-shell +gtk2 gtk3 metacity unity xfce-notify xfwm transparency -unity"
Creating dependencies ...
.. on other use-flags
Some of your useflags may depend on others.
IUSE="gnome-shell +gtk2 gtk3 metacity unity xfce-notify xfwm transparency -unity"
In this example, we need either gtk2 or gtk3 to be enabled. The || defines at-least-one-of
REQUIRED_USE="|| ( gtk2 gtk3 )"
Further on, transparency depends on gtk3
REQUIRED_USE="|| ( gtk2 gtk3 )
transparency? ( gtk3 )"
(The ? indicates: If this useflag is set, require all useflags in the following parenthesis).
... to other packages
Sometimes, a use-flag will enable a feature that requires additional packages.
IUSE="gnome-shell +gtk2 gtk3 metacity unity xfce-notify xfwm transparency -unity"
For example: gnome-shell will need gnome-base/gnome-shell to work.
RDEPEND="gnome-shell? ( gnome-base/gnome-shell )"