# RPOPLPUSH

```json metadata
{
  "title": "RPOPLPUSH",
  "description": "Returns the last element of a list after removing and pushing it to another list. Deletes the list if the last element was popped.",
  "categories": ["docs","develop","stack","oss","rs","rc","oss","kubernetes","clients"],
  "arguments": [{"display_text":"source","key_spec_index":0,"name":"source","type":"key"},{"display_text":"destination","key_spec_index":1,"name":"destination","type":"key"}],
  "syntax_fmt": "RPOPLPUSH source destination",
  "complexity": "O(1)",
  "group": "list",
  "command_flags": ["write","denyoom"],
  "acl_categories": ["@write","@list","@slow"],
  "since": "1.2.0",
  "arity": 3,
  "key_specs": [{"RW":true,"access":true,"begin_search":{"spec":{"index":1},"type":"index"},"delete":true,"find_keys":{"spec":{"keystep":1,"lastkey":0,"limit":0},"type":"range"}},{"RW":true,"begin_search":{"spec":{"index":2},"type":"index"},"find_keys":{"spec":{"keystep":1,"lastkey":0,"limit":0},"type":"range"},"insert":true}],
  "tableOfContents": {"sections":[{"id":"examples","title":"Examples"},{"id":"pattern-reliable-queue","title":"Pattern: Reliable queue"},{"id":"pattern-circular-list","title":"Pattern: Circular list"},{"id":"redis-enterprise-and-redis-cloud-compatibility","title":"Redis Enterprise and Redis Cloud compatibility"},{"id":"return-information","title":"Return information"}]}
}
```













Atomically returns and removes the last element (tail) of the list stored at
`source`, and pushes the element at the first element (head) of the list stored
at `destination`.

For example: consider `source` holding the list `a,b,c`, and `destination`
holding the list `x,y,z`.
Executing `RPOPLPUSH` results in `source` holding `a,b` and `destination`
holding `c,x,y,z`.

If `source` does not exist, the value `nil` is returned and no operation is
performed.
If `source` and `destination` are the same, the operation is equivalent to
removing the last element from the list and pushing it as first element of the
list, so it can be considered as a list rotation command.

## Examples


RPUSH mylist "one"
RPUSH mylist "two"
RPUSH mylist "three"
RPOPLPUSH mylist myotherlist
LRANGE mylist 0 -1
LRANGE myotherlist 0 -1


## Pattern: Reliable queue

Redis is often used as a messaging server to implement processing of background
jobs or other kinds of messaging tasks.
A simple form of queue is often obtained pushing values into a list in the
producer side, and waiting for this values in the consumer side using [`RPOP`](https://redis.io/docs/latest/commands/rpop)
(using polling), or [`BRPOP`](https://redis.io/docs/latest/commands/brpop) if the client is better served by a blocking
operation.

However in this context the obtained queue is not _reliable_ as messages can
be lost, for example in the case there is a network problem or if the consumer
crashes just after the message is received but before it can be processed.

`RPOPLPUSH` (or [`BRPOPLPUSH`](https://redis.io/docs/latest/commands/brpoplpush) for the blocking variant) offers a way to avoid
this problem: the consumer fetches the message and at the same time pushes it
into a _processing_ list.
It will use the [`LREM`](https://redis.io/docs/latest/commands/lrem) command in order to remove the message from the
_processing_ list once the message has been processed.

An additional client may monitor the _processing_ list for items that remain
there for too much time, pushing timed out items into the queue
again if needed.

## Pattern: Circular list

Using `RPOPLPUSH` with the same source and destination key, a client can visit
all the elements of an N-elements list, one after the other, in O(N) without
transferring the full list from the server to the client using a single [`LRANGE`](https://redis.io/docs/latest/commands/lrange)
operation.

The above pattern works even if one or both of the following conditions occur:

* There are multiple clients rotating the list: they'll fetch different 
  elements, until all the elements of the list are visited, and the process 
  restarts.
* Other clients are actively pushing new items at the end of the list.

The above makes it very simple to implement a system where a set of items must
be processed by N workers continuously as fast as possible.
An example is a monitoring system that must check that a set of web sites are
reachable, with the smallest delay possible, using a number of parallel workers.

Note that this implementation of workers is trivially scalable and reliable,
because even if a message is lost the item is still in the queue and will be
processed at the next iteration.

## Redis Enterprise and Redis Cloud compatibility

| Redis<br />Enterprise | Redis<br />Cloud | <span style="min-width: 9em; display: table-cell">Notes</span> |
|:----------------------|:-----------------|:------|
| <span title="Supported">&#x2705; Standard</span><br /><span title="Supported"><nobr>&#x2705; Active-Active</nobr></span> | <span title="Supported">&#x2705; Standard</span><br /><span title="Supported"><nobr>&#x2705; Active-Active</nobr></span> | Deprecated as of Redis v6.2.0. |

## Return information

{{< multitabs id="rpoplpush-return-info" 
    tab1="RESP2" 
    tab2="RESP3" >}}

One of the following:
* [Bulk string reply](../../develop/reference/protocol-spec#bulk-strings): the element being popped and pushed.
* [Nil reply](../../develop/reference/protocol-spec#bulk-strings): if the source list is empty.

-tab-sep-

One of the following:
* [Bulk string reply](../../develop/reference/protocol-spec#bulk-strings): the element being popped and pushed.
* [Null reply](../../develop/reference/protocol-spec#nulls): if the source list is empty.