In Redis, the LMPOP command pops one or more elements from the first non-empty list key from the list of provided key names.

The LMPOP command is similar to LPOP, except that it can accept multiple keys. It’s also similar to BLPOP (which accepts multiple keys), except that it can pop multiple elements (BLPOP can only pop one element).

The LMPOP command was introduced in Redis 7.0.0.

There’s also an BLMPOP command, which is the blocking variant of LMPOP.

Syntax

The syntax goes like this:

LMPOP numkeys key [key ...] LEFT | RIGHT [COUNT count]

The following examples demonstrate this command and its various arguments.

Example

Suppose we create a list like this:

RPUSH scores 1 2 3 4 5 6 7 8 9 10

Result:

(integer) 10

Let’s look at its contents:

LRANGE scores 0 -1

Result:

 1) "1"
 2) "2"
 3) "3"
 4) "4"
 5) "5"
 6) "6"
 7) "7"
 8) "8"
 9) "9"
10) "10"

Here’s an example of using the LMPOP command against that list and another list:

LMPOP 2 oops scores LEFT COUNT 3

Result:

1) "scores"
2) 1) "1"
   2) "2"
   3) "3"

In this case, the oops list was empty, and so LMPOP popped the first three elements from the scores list. As mentioned, LMPOP pops elements only from the first non-empty list key. Seeing as the first list was empty, it popped the specified elements from the second list.

Let’s now use LRANGE to return all remaining elements in the list:

LRANGE scores 0 -1

Result:

1) "4"
2) "5"
3) "6"
4) "7"
5) "8"
6) "9"
7) "10"

The RIGHT Argument

In the previous example I used the LEFT argument. Let’s now use the RIGHT argument:

LMPOP 2 oops scores RIGHT COUNT 3

Result:

1) "scores"
2) 1) "10"
   2) "9"
   3) "8"

Now we’ve popped the last three elements from the list.

Let’s use LRANGE to return all remaining elements in the list:

LRANGE scores 0 -1

Result:

1) "4"
2) "5"
3) "6"
4) "7"

Omit the Count

Here’s what happens when we omit the (optional) COUNT argument and its associated count:

LMPOP 2 oops scores LEFT

Result:

1) "scores"
2) 1) "4"

It popped one element. We specified LEFT and so it popped it from the head of the list.

Let’s do it again from the right:

LMPOP 2 oops scores RIGHT

Result:

1) "scores"
2) 1) "7"

Pop All Elements

Specifying a count that’s either as large or larger than the list pops all elements from the list.

First, let’s take another look at the list:

LRANGE scores 0 -1

Result:

1) "5"
2) "6"

We can pop all elements by specifying a count that’s two or higher.

LMPOP 2 oops scores LEFT COUNT 100

Result:

1) "scores"
2) 1) "5"
   2) "6"