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SET

Sets the value of a key, with optional parameters for expiration and conditions.

Syntax​

SET key value [NX | XX] [GET]

Parameters​

  • key: The name of the key to set.
  • value: The value to set for the specified key.
  • NX: Optional. Set the key only if it does not already exist.
  • XX: Optional. Set the key only if it already exists.
  • GET: Optional. Return the old value stored at the key, or nil if the key did not exist.

Details​

  • Available since: 1.0.0 (basic functionality), 6.2.0 (additional options)
  • Time complexity: O(1)
  • ACL categories: @write, @string, @fast

The SET command sets the value of a key, with various optional parameters that allow for conditional setting and expiration. The command can be used in many scenarios, such as caching, managing time-limited data, or simply storing a value.

Expiration Options​

Expiration is not supported yet.

Conditional Options​

  • NX: Set the key only if it does not already exist.
  • XX: Set the key only if it already exists.

Return Value Option​

  • GET: Return the old value stored at the key before the SET operation. If the key did not exist, return nil.

Examples​

Basic Usage​

To set a simple key-value pair:

SET mykey "Hello, World!"

This will set mykey to "Hello, World!".

Conditional Set (NX)​

To set a key only if it does not already exist:

SET mykey "Hello, Redis!" NX

Conditional Set (XX)​

To set a key only if it already exists:

SET mykey "Hello again!" XX

Using GET Option​

To set a key and return the old value:

SET mykey "Hello, New Value!" GET

This might return:

"Hello, World!"

If mykey did not exist before, it will return nil.

Edge Cases​

  • If NX and XX are both specified, the command will always fail as the conditions are mutually exclusive.
  • If the key exists but is not a string, an error is returned.
  • If the GET option is used and the key did not exist, nil is returned.

RESP2/RESP3 Reply​

  • Simple string reply: OK if the operation was successful.
  • Bulk string reply: the old value stored at the key if the GET option is used, or nil if the key did not exist.