From Gentoo Wiki
Lua is a powerful light-weight programming language designed for extending applications. It can be embedded into various application as scripting language.
USE flags for dev-lang/lua A powerful light-weight programming language designed for extending applications
||make deprecated data structures/routines available|
||Enable support for libreadline, a GNU line-editing library that almost everyone wants|
||Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently)|
||Run the complete (non-portable) testsuite|
emerge --ask dev-lang/lua