-- Usage: redis-cli --eval redis_expire_keys.lua <key-pattern> , <ttl-in-seconds>
local keys = redis.call("keys", KEYS[1])
local toExpire = {}
local i = 1 -- "it is customary in Lua to start arrays with index 1"
for _, key in ipairs(keys) do
    local val = redis.call('ttl', key)
    if val == -1 then
        toExpire[i] = key
        redis.call('expire', key, ARGV[1])
        i = i + 1
    end
end
return toExpire