In Redis, the COPY command copies the value from one key to another.

This command was introduced in Redis 6.2.0.

Syntax

The syntax goes like this:

COPY source destination [DB destination-db] [REPLACE]

Where source is the key that contains the value to copy, and destination is the key to copy it to.

The [DB destination-db] part means that we can optionally specify an alternative logical database index for the destination key. By default, the destination key is created in the logical database used by the connection.

The [REPLACE] part means that we can optionally specify REPLACE to remove the destination key before copying the value to it.

Example

Suppose we set a value:

SET key1 "Dog"

Result:

OK

Now let’s use the COPY command to copy that value to a new key:

COPY key1 key2

Result:

(integer) 1

We get an integer reply of 1, which means that the new key was created and the value was copied.

An integer reply of 0 would mean that it wasn’t copied.

Now let’s check the value of the new key:

GET key2

Result:

"Dog"

As expected, it’s the same value that’s stored in the source key.

Bear in mind that the source key still holds the same value:

GET key1

Result:

"Dog"

When the Destination Key Already Exists

By default, if the destination key already exists, the value is not copied, and we get an integer reply of 0. However, this can be changed by using the REPLACE option.

To test this, let’s change the value of the source key, then try the COPY operation again.

Change the value of the source key:

SET key1 "Cat"

Result:

OK

Now try to copy that key’s value:

COPY key1 key2

Result:

(integer) 0

We get an integer reply of 0, which means that the value wasn’t copied.

We can verify this by checking the value of key2:

GET key2

Result:

"Dog"

It’s still the same value that was set previously.

The REPLACE Option

We can use the REPLACE argument to remove the destination key before copying the value to it. This effectively allows us to copy the value to a key that already exists.

Example:

COPY key1 key2 REPLACE

Result:

(integer) 1

The integer reply of 1 indicates that the value was successfully copied.

Let’s check the value of key2:

GET key2

Result:

"Cat"

Yes, it was successfully copied.