Your first Redis commands

Getting back to the redis-cli prompt

Time for your first Redis commands. In the last lesson we started Redis with Docker and opened a shell, so let's get back to it:

docker exec -it redis redis-cli

You should see the interactive prompt:

127.0.0.1:6379>

Everything in this lesson is typed at that prompt. It is interactive: you type a command, press Enter, and Redis replies right away. No files, no save button. Let's learn four commands.

PING: is Redis there?

We met this one already. It is the quickest way to check the connection:

PING

Redis answers:

PONG

If you see PONG, you are connected and ready. Commands in Redis are not case-sensitive, so PING and ping both work. This course writes them in uppercase by convention.

SET: store a value in Redis

Remember from the first lesson that Redis is a key-value store: a name points to a value. SET creates that link. Store a value under a key:

SET greeting "hello"

Redis replies:

OK

Let's read the parts:

• SET is the command.
• greeting is the key, the name you will look it up by.
• "hello" is the value you are storing.

OK means it worked. You just wrote your first piece of data to Redis.

GET: read a value back by its key

Now ask for it by key:

GET greeting

Redis returns the value:

"hello"

That is the whole loop of a key-value store: SET puts a value in under a key, GET reads it back out. If you GET a key that does not exist, Redis returns (nil), its way of saying "nothing is stored here":

GET missing

(nil)

Watch one edge here: (nil) means the key does not exist, but an empty value is not the same thing. Run SET blank "" and then GET blank, and Redis hands back an empty "", not (nil). The key is there; it just holds nothing. When you check whether something was ever stored, "empty" and "missing" are two different answers.

DEL: remove a value

When you no longer need a key, delete it:

DEL greeting

Redis replies with the number of keys it removed:

(integer) 1

1 means one key was deleted. If the key was not there, you get 0. Read again to confirm it is gone:

GET greeting

(nil)

Gone. You have now created, read, and removed data in Redis.

Common mistake

If your value has a space in it, wrap it in quotes: SET note "buy milk". Without the quotes, Redis treats each word as a separate argument and you get an error about the wrong number of arguments. Single words like hello do not need quotes, but using them is always safe.

What you can do now

With just these four commands you can already store and fetch data. In the next chapter we will go deeper: naming keys well, and making them expire on their own so temporary data cleans itself up.

FAQ

Are Redis commands case-sensitive?

The command names are not: SET and set behave the same. But your keys and values are case-sensitive, so greeting and Greeting are two different keys.

What does (nil) mean?

It means there is no value for that key, either because it was never set or because it was deleted. It is Redis saying "nothing here".

How do I leave the redis-cli prompt?

Type exit or press Ctrl+D. Your Redis container keeps running in the background, so your data stays until you stop the container.

Does SET overwrite an existing key?

Yes. If the key already has a value, SET replaces it with the new one without warning.