Redis Lua script error: Script attempted to access nonexistent global variable 'print' script

Question

I'm learning Lua. Given below, is a Lua script to handle some operations

local function reverseDb ()
  local key =  KEYS[1]
  local value = ARGV[1]
  redis.call('SREM',key,value)
  return value
end

if pcall(reverseDb) then
  print("success")
else
  print("error")
  redis.call('SADD',key,value)
end

While running it throws an error:

Script attempted to access nonexistent global variable 'print' script: 39f13cb3bddd638c815531acbc2dc6434a0329c6, on @user_script:17.

I don't understand why the error is there. Any clue?

Answer 1

Redis runs Lua script in a sandbox context, and limits the usage of global variables, only parts of global variables/functions are allowed. Obviously, print is not allowed.

In your case, you can return the error message instead of printing it.

if pcall(reverseDb) then
  return "success"
else
  redis.call('SADD',key,value)
  return "error"
end