print call issue in Lua based function

Question

I have a Redis 7.x cluster with 3 master nodes running on ports 7000, 7001, 7002. Each master has 1 slave/replica.

I am trying to load and run this Lua based function:

#!lua name=printTestLib
local function printTest(keys, args)
    local time = redis.call('TIME');
    print("current timestamp in millis: " .. time)
end
redis.register_function('printTest', printTest)

When I run it as

127.0.0.1:7000> fcall printTest 0

I see the error:

(error) ERR user_function:4: Script attempted to access nonexistent global variable 'print' script: printTest, on @user_function:4.

What is the issue with the call to print statement?

Answer 1

You're running the Lua based function with print(), which doesn't exist since Redis Lua implementation is sandboxed. You can simply fix this by replacing print with redis.log to log the message you're trying to call.