Strings

The String is the most fundamental Redis data type. Every other data type in Redis is built on top of it. A String value can hold text, integers, floating-point numbers, or raw binary data (such as a serialised JSON payload or an image), up to a maximum of 512 MB per value.

SET and GET

The two most basic commands are SET (store a value) and GET (retrieve it):

127.0.0.1:6379> SET username "alice"
OK
127.0.0.1:6379> GET username
"alice"

Keys are case-sensitive. If you SET a key that already exists, the old value is silently overwritten.

NX and XX Options

SET accepts options to control behaviour when a key already exists:

# NX — only set if the key does NOT exist
127.0.0.1:6379> SET lock "1" NX
OK
127.0.0.1:6379> SET lock "2" NX
(nil)   # key already exists, nothing happened

# XX — only set if the key DOES exist
127.0.0.1:6379> SET lock "3" XX
OK

Integer Operations

When a String value looks like an integer, Redis can increment or decrement it atomically without a read-modify-write cycle in application code:

127.0.0.1:6379> SET page_views 0
OK
127.0.0.1:6379> INCR page_views
(integer) 1
127.0.0.1:6379> INCRBY page_views 10
(integer) 11
127.0.0.1:6379> DECR page_views
(integer) 10
127.0.0.1:6379> DECRBY page_views 3
(integer) 7

INCR is atomic: even if two clients call it simultaneously, each increment is applied without race conditions.

Storing Expiring Strings

You can attach a time-to-live to a string at set time:

# EX sets expiry in seconds
127.0.0.1:6379> SET session_token "abc123" EX 3600
OK
# PX sets expiry in milliseconds
127.0.0.1:6379> SET otp "987654" PX 300000
OK

MSET and MGET

Store or retrieve multiple keys in a single round trip:

127.0.0.1:6379> MSET first_name "Bob" last_name "Smith" city "London"
OK
127.0.0.1:6379> MGET first_name last_name city
1) "Bob"
2) "Smith"
3) "London"

APPEND and STRLEN

127.0.0.1:6379> SET greeting "Hello"
OK
127.0.0.1:6379> APPEND greeting ", World!"
(integer) 13
127.0.0.1:6379> STRLEN greeting
(integer) 13

Strings are the building block for caching, counters, session tokens, and any simple key-value storage need in Redis.