SET & GET

SET and GET — the core of Redis strings

SET key value stores a string. GET key retrieves it. If the key already exists, SET overwrites it unconditionally (unless you add a condition flag).

127.0.0.1:6379> SET city "Bangkok"
OK
127.0.0.1:6379> GET city
"Bangkok"
127.0.0.1:6379> SET city "Chiang Mai"
OK
127.0.0.1:6379> GET city
"Chiang Mai"

SET options

Redis 7 SET supports several options in one command:

Option	Meaning
`EX seconds`	Set expiration in seconds
`PX milliseconds`	Set expiration in milliseconds
`EXAT unix-time-seconds`	Expire at a Unix timestamp (seconds)
`PXAT unix-time-ms`	Expire at a Unix timestamp (milliseconds)
`NX`	Only set if the key does not exist
`XX`	Only set if the key does exist
`GET`	Return the old value before overwriting
`KEEPTTL`	Retain the existing TTL instead of resetting it

127.0.0.1:6379> SET token "abc123" EX 60
OK
127.0.0.1:6379> TTL token
(integer) 59
127.0.0.1:6379> SET counter 0 NX
OK
127.0.0.1:6379> SET counter 99 NX
(nil)
127.0.0.1:6379> GET counter
"0"
127.0.0.1:6379> SET city "Phuket" GET
"Chiang Mai"
127.0.0.1:6379> GET city
"Phuket"

SET token "abc123" EX 60
TTL token
SET counter 0 NX
SET counter 99 NX
GET counter
SET city "Phuket" GET
GET city

SETEX and SETNX

These are older convenience aliases — SET with EX or NX is preferred in Redis 7, but you will still see them in legacy code:

127.0.0.1:6379> SETEX session:user1 3600 "token-xyz"
OK
127.0.0.1:6379> TTL session:user1
(integer) 3599
127.0.0.1:6379> SETNX lock:job1 "worker-A"
(integer) 1
127.0.0.1:6379> SETNX lock:job1 "worker-B"
(integer) 0
127.0.0.1:6379> GET lock:job1
"worker-A"

SETEX session:user1 3600 "token-xyz"
TTL session:user1
SETNX lock:job1 "worker-A"
SETNX lock:job1 "worker-B"
GET lock:job1

MSET and MGET — batch operations

Set or get many keys in a single round-trip. This is significantly faster than individual commands when you need multiple keys at once.

127.0.0.1:6379> MSET user:1:name "Ada" user:1:lang "Python" user:2:name "Bob" user:2:lang "Go"
OK
127.0.0.1:6379> MGET user:1:name user:1:lang user:2:name user:2:lang
1) "Ada"
2) "Python"
3) "Bob"
4) "Go"
127.0.0.1:6379> MGET user:1:name user:99:name
1) "Ada"
2) (nil)

MSET user:1:name "Ada" user:1:lang "Python" user:2:name "Bob" user:2:lang "Go"
MGET user:1:name user:1:lang user:2:name user:2:lang
MGET user:1:name user:99:name

APPEND and STRLEN

APPEND adds to the end of an existing string value (or creates the key if absent). STRLEN returns the byte length of the value.

127.0.0.1:6379> SET log "2024-01-01 boot"
OK
127.0.0.1:6379> APPEND log " | 2024-01-01 ready"
(integer) 34
127.0.0.1:6379> GET log
"2024-01-01 boot | 2024-01-01 ready"
127.0.0.1:6379> STRLEN log
(integer) 34

SET log "2024-01-01 boot"
APPEND log " | 2024-01-01 ready"
GET log
STRLEN log

🟥 SET key val NX — the basis for distributed locks

SET key value NX sets the key only if it does not already exist. It returns OK on success and (nil) if the key was already there. This atomicity makes it the building block for simple distributed locks:

SET lock:resource "worker-id" NX EX 30

If two workers race, only one gets OK. The EX 30 ensures the lock auto-releases after 30 seconds even if the holder crashes.