Lua import library from local path (luasocket) - lua

Question

I'm quite new to Lua and I have some problems with the import mechanism.
From other languages I'm used to do something like this:
include "./lib/mylib.h"
or in general just to pass the local path to the file I would like to include.
Now in Lua it is a bit confusing to me. I read something about that require looks for the library in the lua path.
In my case I would like to create a script that uses the luasocket library but I would like to import it from a local path so that I can deploy it without the need to have it on another machine in the lua path.
From other forums I got solutions like creating a local require function that looks in a given local library folder but that didn't work.
Then I read that I can just type require 'myfile' to import a different file locally but luasocket requires a core.dll and if I just move the lua files of the library to my local path it can't find the dll.
Is there an easy way to solve this. What do I have to do to get this working?

Answer 1

It is sufficient for the .dll extension to be in the LUA_CPATH (so it ends up in package.cpath). For example, put the socket.lua in C:\Foo, and put core.dll in same folder. Then require 'socket' will fail:
> print(package.cpath)
.\?.dll;.\?51.dll;C:\Program Files\Lua\5.1\?.dll;C:\Program Files\Lua\5.1\?51.dl
l;C:\Program Files\Lua\5.1\clibs\?.dll;C:\Program Files\Lua\5.1\clibs\?51.dll;C:
\Program Files\Lua\5.1\loadall.dll;C:\Program Files\Lua\5.1\clibs\loadall.dll
> print(package.path)
;.\?.lua;C:\Program Files\Lua\5.1\lua\?.lua;C:\Program Files\Lua\5.1\lua\?\init.
lua;C:\Program Files\Lua\5.1\?.lua;C:\Program Files\Lua\5.1\?\init.lua;C:\Progra
m Files\Lua\5.1\lua\?.luac
> require 'socket'
.\socket.lua:13: module 'socket.core' not found:
-- look for preload
no field package.preload['socket.core']
-- look for .lua in socket folder anywhere on package.path:
no file '.\socket\core.lua'
no file 'C:\Program Files\Lua\5.1\lua\socket\core.lua'
no file 'C:\Program Files\Lua\5.1\lua\socket\core\init.lua'
...
-- look for .luac in socket folder anywhere on package.path:
no file 'C:\Program Files\Lua\5.1\lua\socket\core.luac'
-- look for .dll in socket folder anywhere on package.cpath:
no file '.\socket\core.dll'
no file '.\socket\core51.dll'
no file 'C:\Program Files\Lua\5.1\socket\core.dll'
no file 'C:\Program Files\Lua\5.1\socket\core51.dll'
no file 'C:\Program Files\Lua\5.1\clibs\socket\core.dll'
no file 'C:\Program Files\Lua\5.1\clibs\socket\core51.dll'
...
stack traceback:
[C]: in function 'require'
.\socket.lua:13: in main chunk
[C]: in function 'require'
stdin:1: in main chunk
[C]: ?
because socket.lua requires socket.core, so Lua interpreter looks for core.lua in a "socket" folder anywhere on package.path, doesn't find it (socket folder doesnt' exist), then looks for core.dll in socket folder anywhere on package.cpath, same problem.
Now create C:\Foo\socket folder, and move core.dll to it, then require 'socket' will work (from interpreter started while cd to C:\Foo).
In your case, if you have yourLuaScript.lua in C:\Foo, you could have socket.lua in same folder, core.dll in C:\Foo\socket, and yourLuaScript.lua could require 'socket' and, as long as package.path contains .\*.lua, and package.cpath contains .\*.dll, you will be able to run yourLuaScript.lua.