The Premake user guide has moved.
For Premake 4.x, the new user guide is here.
For Premake 5.x, the new user guide is here.
This section describes the functions and variables available to Premake scripts.
Premake is built on Lua, so everything in the Lua Reference Manual applies to a Premake script. Premake adds the ability to define solutions, projects, and configurations, as well as functions useful for build configuration tasks.
You may also want to check out LuaForge for a wide assortment of Lua add-on modules.