Lua cannot find installed luarocks on Ubuntu

Question

I install luarocks:

$ sudo apt-get install luarocks

I install lua-cjson by luarocks:

$sudo luarocks install lua-cjson

show packages:

$luarocks list

Installed rocks:
----------------
lua-cjson
   2.1.0-1 (installed) - /usr/local/lib/luarocks/rocks

So, I see package:

$luarocks show lua-cjson

License:    MIT
Homepage:   http://www.kyne.com.au/~mark/software/lua-cjson.php
Installed in:   /usr/local
. . . 
Modules:
    cjson
    lua2json
    json2lua
    cjson.util


    lua-cjson
          2.1.0-1 (installed) - /usr/local/lib/luarocks/rocks

But, Lua can't see the module:

$lua
Lua 5.2.3  Copyright (C) 1994-2013 Lua.org, PUC-Rio
> require "cjson"
stdin:1: module 'cjson' not found:
....


$locate cjson.so
 /usr/local/lib/lua/5.1/cjson.so

What it is the error??

Womanly

Answer 1

The problem seems to be that luarocks by default installs things for Lua 5.1 (this is the behavior if you installed it using apt-get). If you don't mind using Lua 5.1, you can just use that instead (by typing lua5.1), and require "cjson" should work fine.

If you really want cjson for Lua 5.2, it's a bit more complicated. First, you need to make sure that you have the development files for Lua 5.2. Try

sudo apt-get install liblua5.2-dev

Then download the latest version of the source for luarocks here. Extract, and cd to the directory in a terminal.

Then do the following commands (from this post)

./configure --lua-version=5.2 --versioned-rocks-dir
make build
sudo make install

This will install a version of luarocks which works with Lua 5.2. You can then install cjson using

sudo luarocks-5.2 install lua-cjson

You should then be able to use cjson in Lua 5.2.

Pomelo

Thanks for this solution! This really helps with the installation of the correct luarocks version, as the default in Ubuntu 18.04 is still outdated and uses Lua 5.1 – Concordant