• Function is deprecated. It is easy to set up a module with regular Lua code. Modules are not expected to set global variables.
• Functions setfenv and getfenv were removed, because of the changes in environments.
• Function math.log10 is deprecated. Use with 10 as its second argument, instead.
• Function table.maxn is deprecated. Write it in Lua if you really need it.
• Function os.execute now returns true when command terminates successfully and nil plus error information otherwise.
• Function unpack was moved into the table library and therefore must be called as table.unpack.
• The table package.loaders was renamed package.searchers.
• Lua does not have bytecode verification anymore. So, all functions that load code ( and loadfile) are potentially insecure when loading untrusted binary data. (Actually, those functions were already insecure because of flaws in the verification algorithm.) When in doubt, use the argument of those functions to restrict them to loading textual chunks.
• The standard paths in the official distribution may change between versions.