This is my eval command
eval "local b = redis.call('hget', 'foo', 'baz'); if (type(b) == 'boolean') then return 'boolean' else return 'not a boolean' end" 0 "hello"
This returns boolean. But if I return the value of b I get (nil). What is happening here?
From https://gigacrunch.herokuapp.com/commands/hget
the value associated with field, or nil when field is not present in the hash or key does not exist
There are some conversion rules between Redis an Lua values https://cndoc.github.io/redis-doc-cn/cn/commands/eval.html
Redis nil is converted to Lua false. So b is false. Hence type(b) is boolean so you return a string 'boolean'.
If you return b you return false. Lua false is converted to Redis nil.