Returns the length of the list stored at key.
If key does not exist, it is interpreted as an empty list and 0 is returned.
An error is returned when the value stored at key is not a list.
*Return value
Integer reply: the length of the list at key.
*Examples
redis>
LPUSH mylist "World"
(integer) 1redis> LPUSH mylist "Hello"
(integer) 2redis> LLEN mylist
(integer) 2