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RPOPLPUSH

Removes the last element from a list and adds it to the beginning of another list.

Syntax​

RPOPLPUSH source destination

Parameters​

  • source: The key of the list from which the element will be removed.
  • destination: The key of the list to which the element will be added.

Details​

  • Available since: 1.0.0
  • Time complexity: O(1)
  • ACL categories: @write, @list, @fast

The RPOPLPUSH command performs a combination of two operations:

  1. Removes the last element from the source list.
  2. Adds the removed element to the beginning of the destination list.

If source does not exist or is empty, the command returns nil and no changes are made. If destination does not exist, it is created as an empty list before the element is added.

Examples​

Basic Usage​

Assume we have the following lists:

RPUSH mylist1 "a" "b" "c"
RPUSH mylist2 "x" "y"

To move the last element from mylist1 to the beginning of mylist2:

RPOPLPUSH mylist1 mylist2

After running this command:

  • mylist1 will contain: a b
  • mylist2 will contain: c x y

The returned value will be:

"c"

Source List is Empty​

If mylist1 was already empty:

RPOPLPUSH mylist1 mylist2

The command will return:

(nil)

And mylist2 will remain unchanged.

Destination List Does Not Exist​

If mylist2 did not exist before:

RPOPLPUSH mylist1 mylist2

mylist2 will be created and will contain the element that was removed from mylist1.

Edge Cases​

  • If source does not exist or is empty, RPOPLPUSH will return nil and no changes will be made to destination.
  • If destination is the same as source, the element will be removed from the end of the list and added to the beginning of the same list.

RESP2/RESP3 Reply​

  • Bulk string reply: the element that was removed from the source list and added to the destination list. If the source list is empty or does not exist, the reply is nil.