I'm new to redis/nginx combinations, however I think you should also add following modules:
-https://github.com/agentzh/lua-redis-parser
-https://github.com/chaoslawful/lua-nginx-module.

Then you can use

content_by_lua '
local replies = ngx.location.capture("/redis2")
local parser = require('redis.parser')
-- assuming the replies variable holds n redis responses
-- to be parsed:
local results = parser.parse_replies(replies, n)
for i, result in ipairs(results) do
local res = result[1]
local typ = result[2]
-- res and typ have exactly the same meaning as in
-- the parse_reply method documented above
end
'