Introduction to Redis

Redis is much more than a key-value store; it offers several data structures that can be used. This introduction will cover the basics of how to use Redis.

Installing Redis

Download and extract the code:

curl -O http://redis.googlecode.com/files/redis-2.0.0-rc1.tar.gz
tar -xzvf redis-2.0.0-rc1.tar.gz
cd redis-2.0.0-rc1

Compile and install:

make
sudo cp redis-server redis-cli redis-benchmark /usr/local/bin/

Delete the source code (optional):

cd ..
rm -rf redis-2.0.0-rc1
rm redis-2.0.0-rc1.tar.gz

Starting Redis

Use an instance provided by Redis To Go or start a local Redis instance. For either, you need the hostname, port, and password listed below to connect to Redis.

To start a local instance:

redis-server

By default, the port is 6379 and there is no password.

Using Redis

Start the redis-cli with the hostname, port, and password

redis-cli -h my-host -p 1234 -a mypassword

If you are using a local instance, the host is localhost, the default port is 6379, and there is no password by default.

redis-cli

GET and SET

Redis is a key-value store. By issuing the command SET foo bar you set the value of foo to bar.

For example, issue the following command from the redis-cli you just started.

redis> set foo bar
OK

Now read the value of foo with the GET command.

redis> get foo
"bar"

EXPIRE and TTL

You can set keys to expire in a given amount of time by using the command, EXPIRE. TTL reports the time remaining before the key expires.

redis> set foo bar
OK
redis> expire foo 120
(integer) 1
redis> ttl foo
(integer) 113

Lists

One of the distinguishing features of Redis is that the values of a key can be data-structures, rather than just values.

The following commands pertain to lists: RPUSH, LPUSH, LLEN, LRANGE, LTRIM, LINDEX, LSET, LREM, LPOP, RPOP, BLPOP, BRPOP, RPOPLPUSH, and SORT.

To create a list use LPUSH or RPUSH. If a list already exists, LPUSH will add the given value to the beginning of the list and RPUSH will add it to the end.

redis> lpush cities "San Francisco"
(integer) 1
redis> lpush cities "Boston"
(integer) 2
redis> lrange cities 0 -1
1. "San Francisco"
2. "Boston"
redis> sort cities alpha
1. "Boston"
2. "San Francisco"
redis> rpop cities
"San Francisco"
redis> lrange cities 0 -1
1. "Boston"

The SORT command sorts the list lexicographically in ascending order with the ALPHA argument. To sort in descending order, append the DESC argument to the SORT command.

The RPOP command pops an element from the list's end. LPOP pops an element from the list's beginning.

For more information about the list command, see the Redis reference

Sets

Sets are similar to lists, except each element can occur only once. The following commands pertain specifically to sets: SADD, SREM, SPOP, SMOVE, SCARD, SISMEMBER, SINTER, SINTERSTORE, SUNION, SUNIONSTORE, SDIFF, SDIFFSTORE, SMEMBERS, SRANDMEMBER.

redis> sadd states "Vermont"
(integer) 1
redis> smembers states
1. "Vermont"
redis> sadd states "Texas"
(integer) 1
redis> scard states
(integer) 2
redis> sadd states "Vermont"
(integer) 0
redis> smembers states
1. "Vermont"
2. "Texas"
redis> sadd states "California"
(integer) 1
redis> smembers states
1. "Vermont"
2. "Texas"
3. "California"
redis> srem states "California"
(integer) 1
redis> smembers states
1. "Vermont"
2. "Texas"

The SADD command adds an item to the set, unless the item already exists in the set. If the item does not exist, it is added and 1 is returned; otherwise, 0 is returned. SMEMBERS returns all items in the set. SCARD returns the cardinality of the set. SREM removes an item from the list.

Hashs

Using a hash, you can assign values to fields in each key.The following commands operate on sets: HSET, HGET, HSETNX, HMSET, HMGET, HINCRBY, HEXISTS, HDEL, HLEN, HKEYS, HVALS, HGETALL.

redis> hset user name "John Doe"
(integer) 1
redis> hget user name
"John Doe"
redis> hset user address "1234 Lombard Street"
(integer) 1
redis> hget user address
"1234 Lombard Street"
redis> hgetall user
1. "name"
2. "John Doe"
3. "address"
4. "1234 Lombard Street"

In the example above, the name of user is set to "John Doe" using the HSET command. The HGET command is used to get the name value of user. HGETALL returns all the keys and values related to the specified key.

Conclusion

For additional commands, see the Redis Command Reference.