In Redis, the APPEND command appends a given value to the end of the value of a specified key.

If the key doesn’t exist, APPEND creates the key with the empty string and appends the value to it (so it basically works like the SET command in this case).

Syntax

APPEND key value

Where key is the key to append to, and value is the value to append.

Example

Suppose we set a key like this:

SET pets "Cat"

Result:

OK

Let’s quickly take a look at it:

GET pets

Result:

"Cat"

OK, now let’s append a value to it:

APPEND pets " Dog"

Result:

(integer) 7

In this case we get an integer reply of 7, which is the length of the string after the APPEND operation was performed.

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

GET pets

Result:

"Cat Dog"

Our new string has been appended.

Note that the only reason there’s a space between the two values is because I included a space at the left of the string to be appended. If I hadn’t done that, the two strings would have been joined with no space between them.

Extract a Value

We can use the GETRANGE command to extract a specified part of the value of a given key. Therefore, if we’ve appended multiple values to a string, and we know how long they are, we can use GETRANGE to extract a value based on its position in the overall string:

GETRANGE pets 4 6

Result:

"Dog"

When the Key Doesn’t Exist

As mentioned, if the key doesn’t exist, APPEND creates the key with the empty string and appends the value to it (so it basically works like the SET command).

Example:

APPEND newkey "Dog"

Result:

(integer) 3

Let’s check the value of the newkey key:

GET newkey

Result:

"Dog"