In Redis, the SMOVE command moves a member of a set from one key to another. In other words, the member is removed from the source set and added to the destination set.

If the destination set doesn’t already exist, it’s created and the member is moved to it. If the source set doesn’t exist, no operation is performed, and an integer reply of 0 is returned.

Syntax

The syntax goes like this:

SMOVE source destination member

So this means that we specify the source key, the member to move, and the destination key when calling the command.

Example

Suppose we create the following set:

SADD todo Bob Kate Jim Ash

We can use SMEMBERS to see all the members of the set:

SMEMBERS todo

Result:

1) "Kate"
2) "Ash"
3) "Jim"
4) "Bob"

Now let’s use the SMOVE command to move one of those members to a new key:

SMOVE todo done Jim

Result:

(integer) 1

We get an integer reply of 1, which means that one member was moved to the destination set.

Let’s check the source set again:

SMEMBERS todo

Result:

1) "Kate"
2) "Ash"
3) "Bob"

We can see that Jim is no longer in the source set.

Let’s check the destination set:

SMEMBERS done

Result:

1) "Jim"

The member is now in the destination set.

When I ran SMOVE above, the destination set didn’t exist. Therefore, it was created and the member was moved to it.

When we say that it was moved, it was removed from the source set and added to the destination set.

Non-Existent Source Key

Specifying a source key that doesn’t exist results in no operation being performed, and an integer reply of 0 being returned:

SMOVE oops done Kate

Result:

(integer) 0

Non-Existent Member

It’s the same when specifying a member that doesn’t exist. No operation is performed, and an integer reply of 0 is returned:

SMOVE todo done Eduardo

Result:

(integer) 0

Passing the Wrong Number of Arguments

Passing the wrong number of arguments results in an error:

SMOVE todo done Kate Ash

Result:

(error) ERR wrong number of arguments for 'smove' command

The error tells us what we did wrong.

We get the same error if we call the command without any arguments:

SMOVE

Result:

(error) ERR wrong number of arguments for 'smove' command

SMOVE is Atomic

The SMOVE operation is atomic, which means that at any point in time, the member will always appear to other clients as a member of either the source set or the destination set.