Inspecting keys and values

How to check the value of a Redis key

You found a key with SCAN. Now you want to check its value. The catch: you cannot just GET everything. GET only works on strings, and Redis throws an error if you point it at a list or a hash. So to read the value of a Redis key you first figure out what type of key it is, then reach for the matching command.

Check if a key exists and what type it holds

EXISTS tells you if a key is there. It returns 1 for yes, 0 for no:

127.0.0.1:6379> EXISTS user:42:name
(integer) 1

TYPE tells you which data type it holds:

127.0.0.1:6379> TYPE user:42:name
string

Possible answers are string, hash, list, set, and zset (a sorted set), the types you met in Core data types. The type decides which read command to use.

How long until it expires

TTL shows the remaining time to live in seconds:

127.0.0.1:6379> TTL session:abc
(integer) 274

Two answers are special and worth memorising:

• -1 means the key exists but has no expiry, it lives forever.
• -2 means the key does not exist (it may have already expired).

We covered this in Expiration and TTL; TTL is how you check it from the console.

Reading the value, by type

Once TYPE tells you what you have, use the matching command:

string   GET key
hash     HGETALL key
list     LRANGE key 0 -1
set      SMEMBERS key
zset     ZRANGE key 0 -1 WITHSCORES

Some real output:

127.0.0.1:6379> GET user:42:name
"Ada"

127.0.0.1:6379> HGETALL user:42
1) "name"
2) "Ada"
3) "email"
4) "ada@example.com"

127.0.0.1:6379> LRANGE queue:emails 0 -1
1) "job-1"
2) "job-2"

127.0.0.1:6379> SMEMBERS tags:post:9
1) "redis"
2) "php"

127.0.0.1:6379> ZRANGE leaderboard 0 -1 WITHSCORES
1) "ada"
2) "10"
3) "bob"
4) "25"

The 0 -1 on lists and sorted sets means "from the first element to the last": 0 is the first index and -1 is the last, so it reads the whole thing. WITHSCORES asks the sorted set to include each member's score next to it.

Worth remembering: LRANGE key 0 -1 on a huge list is the same trap as KEYS *. It is an O(N) call that has to serialize every element in one pass, and Redis is busy the whole time. On a list with a handful of items it is nothing; on one holding a million jobs it stalls the server. When you only need a peek, ask for a slice, like LRANGE queue:emails 0 9 for the first ten.

Going deeper: encoding and memory

Two commands help when you care about performance or size.

OBJECT ENCODING reveals how Redis stores the value internally:

127.0.0.1:6379> OBJECT ENCODING user:42
"listpack"

Small hashes, lists, and sets use compact encodings like listpack or intset to save memory; they switch to a bigger encoding once they grow. You rarely need this, but it is useful when tuning.

MEMORY USAGE reports how many bytes a key takes, including its overhead:

127.0.0.1:6379> MEMORY USAGE user:42
(integer) 104

Handy when hunting for keys that eat too much RAM.

Common mistake

Running GET on a key that is not a string. If GET returns:

(error) WRONGTYPE Operation against a key holding the wrong kind of value

you skipped the TYPE check. Always ask TYPE first, then pick the right read command from the table above.

FAQ

How do I check what type a Redis key is?

Run TYPE key. It returns string, hash, list, set, or zset, which tells you whether to read it with GET, HGETALL, LRANGE, SMEMBERS, or ZRANGE.

How do I read a whole list or sorted set in Redis?

Use LRANGE key 0 -1 for a list and ZRANGE key 0 -1 WITHSCORES for a sorted set. The 0 -1 range means first element to last, so you get everything.

What does TTL -1 or -2 mean?

-1 means the key exists but never expires. -2 means the key does not exist at all (often because it already expired).

Why does GET return a WRONGTYPE error?

Because the key is not a string. GET only reads strings. Check TYPE first, then use the matching command for that type.