Redis Commands

Organizing frequently used Redis commands

1. GET key

• A command to retrieve the value of a key

• If the key does not exist, it returns nil

2. SET key value

• A command to SET a key with a string value

• If the key already has a value set, it overwrites it

Options

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

• EX seconds

  • Can set the expire time (in seconds)

• PX milliseconds

  • Set the expire time (in milliseconds)

• NX

  • Setting to SET only when the key does not exist

• XX

  • Setting to SET only when the key exists

• KEEPTTL

  • Setting to keep the TTL that the key has

• GET

  • If the key already exists,

    • Returns the set value

  • If the key does not exist,

    • Returns nil

Return value

• Returns OK if the key is successfully SET

Examples

redis> SET haha "hoho"
OK
redis> GET haha
hoho

3. GETSET key value

• SETs a value for the key and returns the previously stored value

• Returns Error if the key exists but has no stored string value

Examples

redis> del haha
1
redis> SET haha "hoho"
OK
redis> GETSET haha "yay"
hoho
redis> GET haha
yay

4. EXPIRE key seconds

• Sets a timeout on the key

  • When the timeout expires, the key is automatically deleted

• The set timeout is cleared when the key's content is deleted or overwritten

  • The following commands clear the timeout:

    • DEL

    • SET

    • GETSET

    • All *STORE commands

  • That is, all other commands that alter values do not change the timeout

    • ex) The INCR command that increments a value does not affect the timeout

• The timeout can be cleared by converting the key to a persistent key through the PERSIST command

• Note that calling the EXPIRE command with a non-positive timeout deletes the key rather than expiring it!

  • The key event is del, not expired

Refreshing expires

• You can call the EXPIRE command on a key that already has an expire set to configure a new timeout

  • In this case, the TTL (Time to Live) is updated to the newly set value

Return value

• Returns 1 if the timeout is set

• Returns 0 if the key does not exist

Examples

redis> EXPIRE haha 10
1
redis> TTL haha
6
redis> del haha
0
redis> SET haha "hoho"
OK
redis> EXPIRE haha 10
1
redis> TTL haha
8
redis> SET haha "hohohoho"
OK
redis> TTL haha
-1

5. TTL key

• Returns the TTL (Time To Live) of the timeout set on the key

  • Returns -2 if the key does not exist

  • Returns -1 if the key exists but no expire is set

6. INCRBY key increment

• Increments the number stored at the key

• If the key does not exist, sets it to 0 before executing the increment

Return value

• Returns the incremented value

• Returns Error if the key has a value of the wrong type that cannot be converted to an integer

Examples

redis> SET num 10
OK
redis> INCRBY num 25
35
redis> SET string "10"
OK
redis> INCRBY string 5
15
redis> SET wrong "wrong value"
OK
redis> INCRBY wrong 10
ERR value is not an integer or out of range

7. DECRBY key decrement

• Decrements the number stored at the key

• If the key does not exist, sets it to 0 before executing the decrement

Return value

• Returns the decremented value

• Returns Error if the key has a value of the wrong type that cannot be converted to an integer

Examples

redis> SET num "10"
OK
redis> DECRBY num 4
6

More to be added