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SET

Sets key to hold a string value. If key already exists, its value is overwritten.

Syntax

SET key value [NX | XX] [EX seconds | PX milliseconds | EXAT timestamp | PXAT timestamp | KEEPTTL] [GET]

Arguments

Argument Type Description
key string The key to set.
value string The value to store.
NX flag Only set the key if it does not already exist.
XX flag Only set the key if it already exists.
EX seconds integer Set expiry as a relative duration in seconds.
PX milliseconds integer Set expiry as a relative duration in milliseconds.
EXAT timestamp integer Set expiry as an absolute Unix timestamp in seconds.
PXAT timestamp integer Set expiry as an absolute Unix timestamp in milliseconds.
KEEPTTL flag Keep the existing TTL when overwriting the value.
GET flag Return the old value before setting. Returns nil if the key did not exist.

Mutual exclusivity:

  • NX and XX cannot be used together.
  • EX, PX, EXAT, PXAT, and KEEPTTL are mutually exclusive — only one may be provided.

Return value

  • OK on success.
  • The old value (or nil if the key didn't exist) when GET is specified.
  • nil when NX or XX condition is not met.

Errors

  • missing arguments — fewer than two arguments provided.
  • syntax error — unknown option, duplicate option, or conflicting options.
  • invalid expire time in 'set' command — expiry value is not a valid positive integer.

Examples

> SET name helix
OK

> SET session abc123 EX 3600
OK

> SET token xyz PX 5000
OK

> SET event log EXAT 9999999999
OK

> SET event log PXAT 9999999999000
OK

Set only if the key does not exist:

> SET name helix NX
nil

> SET newkey value NX
OK

Set only if the key already exists:

> SET name helix XX
OK

> SET ghost value XX
nil

Keep the existing TTL when updating the value:

> SET name helix EX 3600
OK

> SET name updated KEEPTTL
OK

Return the old value while setting a new one:

> SET name helix
OK

> SET name world GET
helix

> SET nonexistent value GET
nil