20 Redis String Commands Examples using redis-cli and Python Library

Redis is an in-memory key-value pair database.

Redis is extremely fast, as the operation happens in the memory. Redis also provides on-disk persistence and built-in replication.

In Redis, you can use these data structures: 1) String 2) Hash 3) List 4) Set 5) Sorted Set.

There is no integer or float data type in Redis. But, you can use string as integer, and there are few String commands that will allow you to manipulate string values are numbers.

In this tutorial, we’ll explain all the following Redis string (and number) commands with examples.

In our examples, we’ll explain both redis-cli and Redis Python Library version of these string commands.

• SET and GET
• SETEX and PSETEX
• SETNX and SETXX
• DEL
• APPEND
• STRLEN
• SETRANGE and GETRANGE
• INCR, INCRBY and INCRBYFLOAT
• DECR and DECRBY
• MSET and MGET
• MSETNX

Redis CLI and Python examples

This article explains all the Redis string commands using the following two methods: 1) Redis CLI 2) Redis Python Library

Redis CLI

You can start the Redis command line interface using “redis-cli” command. On your server, when you type redis-cli, you’ll get a Redis command line prompt as shown below. In this prompt you can type any Redis commands.

# redis-cli
127.0.0.1:6379>

In the above:

• redis-cli is the command that you type on Linux prompt to start the Redis command line interface
• 127.0.0.1:6379> – This is the redis prompt where you can type all Redis commands. 6379 is the default port on the local server (127.0.0.1) where the Redis server is running.

Redis Python Library

You can also use Redis from several programming language. In our tutorial, we’ll show how to use Redis string commands in Python.

For this, you should import the Redis library inside your Python program, and then create a connection to the server, and then using that redis connection, call the Redis commands.

# python
>>> import redis;
>>> con = redis.Redis("localhost");

In the above:

• python is the command that you type on Linux prompt to start the python command line interface.
• >>> is the python prompt where you type python commands.
• import redis; – This is the python command to import redis library before we can start using redis command.
• con = redis.Redis(“localhost”); – Using the redis python library, we are creating a new connection to Redis server. We’ll be using this “con” connection inside python to call Redis commands.

If you are using PHP: How to Use Redis with PHP using PhpRedis with Examples

1. SET: Assign Value to a Key

Using SET command, you can assign a value to a key as shown below.

127.0.0.1:6379> SET site "thegeekstuff"
OK

In the above:

• SET is the redis command from redis-cli
• site is the name of the key
• “thegeekstuff” is the value that we are assigning to site.

In Python:

>>> con.set("site","thegeekstuff");
True

Note: In the python redis library, for all the redis commands, you need to specify the name of the key within double quotes. If not, you’ll get the “NameError: name is not defined” error.

>>> con.set(site,"thegeekstuff");
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'site' is not defined

2. GET: Retrieve Value from a Key

Using GET command, you can retrive the value from a key as shown below.

127.0.0.1:6379> GET site
"thegeekstuff"

If a key doesn’t exist, you’ll see “nil” as the output.

127.0.0.1:6379> GET forum
(nil)

In Python:

>>> con.get("site");
'thegeekstuff'

Note: For ALL redis string commands, when you are trying to manipulate a key that is of a different datatype (anything other than string), then you’ll get the following WRONGTYPE error message. This just means that the key that you are using is not of string datatype.

127.0.0.1:6379> GET multiplesites
(error) WRONGTYPE Operation against a key holding the wrong kind of value

3. SET..EX, SETEX, EXPIRE: Expire the Key in X Seconds

You can also expire the value of the key after a certain time. For this, use the EX option (EX stands for Expire) in the SET command as shown below.

In the following example, the value of the key site is set and it will expire after 10 seconds.

127.0.0.1:6379> SET site "thegeekstuff" EX 10
OK

Note: The above SET .. EX option is available only From Redis 2.6.12 version.

You can also use SETEX command to set the EX value in seconds as shown below. But, Redis recommends that you start using the above SET..EX option, as SETEX might be deprecated in the future.

127.0.0.1:6379> SETEX site 10 "thegeekstuff"
OK

Another option to expire a key is to use EXPIRE command as shown below. The following will expire the site key in 10 seconds.

127.0.0.1:6379> SET site "thegeekstuff"
OK

127.0.0.1:6379> EXPIRE site 10
(integer) 0

In Python use set command with ex parameter as shown below.

>>> con.set("site","thegeekstuff",ex=10);
True

In Python you can also use setex command:

>>> con.setex("site","thegeekstuff",10);
True

4. SET..PX, PSETEX: Expire the Key in X milliseconds

Instead of expiring a key in seconds, you can also expire a key in milliseconds using PX option while setting the value using SET command as shown below.

In the following example, the value of the key site is set and it will expire after 100 milliseconds.

127.0.0.1:6379> SET site "thegeekstuff" PX 100
OK

You can also use PSETEX command to set the PX value in milliseconds as shown below. But, Redis recommends that you start using the above SET..PX option, as PSETEX might be deprecated in the future.

127.0.0.1:6379> PSETEX site 100 "thegeekstuff" 
OK

Note: There is no SETPX command in Redis. Instead, use the above PSETEX command.

In Python use set command with px parameter as shown below.

>>> con.set("site","thegeekstuff",px=100);
True

5. SET..NX, SETNX: Set Value ONLY When Key doesn’t Exist

SET command by default will overwrite the previous value, if you try to set the same key again. As you see below, we’ve overwritten the value of site key with new value.

127.0.0.1:6379> SET site "thegeekstuff (NEW)"
OK

127.0.0.1:6379> GET site
"thegeekstuff (NEW)"

But, if a key exists, and you don’t want to overwrite the value, then use the NX option with SET command as shown below.

First, let us set the value back to original.

SET site "thegeekstuff"

Next, Use the NX option along with SET command as shown below.

127.0.0.1:6379> SET site "thegeekstuff (NEW)" NX
(nil)

As you see from the above output, it didn’t say OK, it said “(nil)”, which means that the SET command didn’t change any value.

As you see below, the value of site key didn’t change.

127.0.0.1:6379> GET site
"thegeekstuff"

You can also use SETNX command which does exactly the same as the above SET..NX. In the following example, since the site key already exists, it didn’t set the new value.

127.0.0.1:6379> SETNX site "thegeekstuff (NEW)"
(integer) 0

In Python:

>>> con.set("site","thegeekstuff (NEW)",nx=True);

>>> con.setnx("site","thegeekstuff (NEW)");
False

>>> con.get("site");
'thegeekstuff'

6. SET..XX: Set Value ONLY When Key Exist

In the following example, we’ll set the value for the key “blog” only if that key exists previously.

Since this is the first time we are setting the value for the key blog, it failed as shown below.

127.0.0.1:6379> SET blog "thegeekstuff" XX
(nil)

127.0.0.1:6379> GET blog
(nil)

In the following example, we’ll set a new value for the key “site” only if that key exists previously.

Since we already had the key site, the new value was set properly as shown below.

127.0.0.1:6379> SET site "thegeekstuff (NEW)" XX
OK

127.0.0.1:6379> GET site
"thegeekstuff (NEW)"

In Python:

>>> con.set("blog","thegeekstuff",xx=True);

7. DEL: Delete a Key

DEL will delete the given key. The output will indicate how many keys it has deleted. In this example, the output is an interger value of 1, which indicates that it has deleted 1 key.

127.0.0.1:6379> GET site
"thegeekstuff"

127.0.0.1:6379> DEL site
(integer) 1

If the given key doesn’t exist, it wil simply ignore it. As you see below, the output is an interger value of 0, which indicates that it didn’t delete any key.

127.0.0.1:6379> DEL site
(integer) 0

You can also delete multiple keys in a single DEL command as shown below.

The output of the following command is an integer value of 2, which indicates that it has deleted 2 keys. This is because we never had a key called “forum”.

127.0.0.1:6379> DEL site blog forum
(integer) 2

In Python, when delete is successful:

>>> con.delete("site");
1

In Python, when key doesn’t exist, delete returns 0:

>>> con.delete("site");
0

In Python, you can also use delete command to delete multiple keys:

>>> con.delete("site","blog","forum");
2

8. APPEND: Append Given Value to an Existing Value of a Key

APPEND command will append the given value to the end of the existing value for a key.

First, set an initial value to the site key.

127.0.0.1:6379> SET site "the"
OK

Next, use the APPEND command to append value to an existing key. The output of the APPEND command will display the total number of characters in the string after the APPEND is completed.

127.0.0.1:6379> APPEND site "geek"
(integer) 7

127.0.0.1:6379> APPEND site "stuff"
(integer) 12

127.0.0.1:6379> GET site
"thegeekstuff"

If a key doesn’t exist previously, APPEND command behave like a SET command and will assign the value to the key as shown below. In this example, we never had a key called forum.

127.0.0.1:6379> APPEND forum "TGS"
(integer) 3

127.0.0.1:6379> GET forum
"TGS"

In Python:

>>> con.set("site","the");
True

>>> con.append("site","geek");
7L

>>> con.append("site","stuff");
12L

>>> con.get("site");
'thegeekstuff'

9. STRLEN: Get the Lenght of the Value of a Key

STRLEN command will get the number of characters in the value. Basically this will return the lenght of the string value stored in the given key as shown below.

127.0.0.1:6379> GET site
"thegeekstuff"

127.0.0.1:6379> STRLEN site
(integer) 12

127.0.0.1:6379> GET forum
"TGS"

127.0.0.1:6379> STRLEN forum
(integer) 3

When a key doesn’t exist, it will return 0 as shown below. In this example, we don’t have a key called database.

127.0.0.1:6379> STRLEN database
(integer) 0

In Python:

>>> con.strlen("site");
12

10. SETRANGE: Replace Part of the Value (Substring Replace Operation)

For this example, we’ll use the following distro string that has the value as “Linux OS”

127.0.0.1:6379> SET distro "Linux OS"
OK

127.0.0.1:6379> GET distro
"Linux OS"

Using SETRANGE command, we can replace part of the string starting from a speficied offset value until the end of the string.

In the following example, the values starting from offset 6 until the end of the string (which in the above example is “OS”) will be replaced by the given string (“Operating System”)

The output of the SETRANGE command will the total number of characters in the key after the SETRANGE is completed.

127.0.0.1:6379> SETRANGE distro 6 "Operating System"
(integer) 22

127.0.0.1:6379> GET distro
"Linux Operating System"

Note: When you calculating the string position, the offset starting value is 0. i.e Start counting from 0.

In Python:

>>> con.set("distro","Linux OS");
True

>>> con.setrange("distro",6,"Operating System");
22

>>> con.get("distro");
'Linux Operating System'

11. GETRANGE: Retrieve Part of the Value (Get Substring Operation)

The following example will get the substring starting from offset 3 until offset 6.

127.0.0.1:6379> GET site
"thegeekstuff"

127.0.0.1:6379> GETRANGE site 3 6
"geek"

Two things to keep in mind:

• The offset value for the 1st character in the string is 0 (and not 1).
• The last value in the GETRANGE is not the total number of characters to extract. It is the offset value (the location) of the last character (until which) that you want extract.

You can also give negative value for the offset, which will be calculated from the last position. For example, offset of -1 indicates the last character, -2 indicates the 2nd character from last, etc.

The following example will extract the last 5 characters. i.e Starting from offset -5 until offset -1.

127.0.0.1:6379> GETRANGE site -5 -1
"stuff"

Again, please note that the 1st character position is offset 0, and the last character position represented by negative offset value is -1. So, the following example will start from 1st position until the last position, giving us the whole string back.

127.0.0.1:6379> GETRANGE site 0 -1
"thegeekstuff"

If the last offset (end offset) is way out of range (i.e greater than the total number of characters in the string), it will get until the end of the string. In the following example, offset value of 25 is greater than the total number of characters in the string. So, it started from offset 7 and extracted the values until the end of the string.

127.0.0.1:6379> GETRANGE site 7 25
"stuff"

In Python:

>>> con.getrange("site",3,6);
'geek'

>>> con.getrange("site",-5,-1);
'stuff'

>>> con.getrange("site",0,-1);
'thegeekstuff'

>>> con.getrange("site",7,25);
'stuff'

12. GETSET: Set New Value and Return Old Value

As the name implies, GETSET is a combination of GET and SET command. So, it GETs the old value first and displays it. After that, it sets the given value to the key.

127.0.0.1:6379> GETSET site "The Geek Stuff Website"
"thegeekstuff"

127.0.0.1:6379> GET site
"The Geek Stuff Website"

In Python:

>>> con.getset("site","The Geek Stuff Website");
'thegeekstuff'

>>> con.get("site");
'The Geek Stuff Website'

13. INCR: Increment the Value by One

As we explained earlier, there is no number concept in Redis datatypes. Redis doesn’t have interger or float datatype. Redis will use string values as integers using string related commands that are specifically designed to manipulate numbers inside a string value.

This increments the value of the given key by one. The output of the INCR command will be the final value of the key after the increment.

127.0.0.1:6379> SET count 5
OK

127.0.0.1:6379> INCR count
(integer) 6

127.0.0.1:6379> GET count
"6"

Note:When you try to increment an existing key that has a string value, you’ll get the following error message.

127.0.0.1:6379> GET site
"thegeekstuff"

127.0.0.1:6379> INCR site
(error) ERR value is not an integer or out of range

Also, when you try to increment a key that doesn’t exist, it will create that key, set the value to 0, and then increment it by one as shown below.

127.0.0.1:6379> GET stat
(nil)

127.0.0.1:6379> INCR stat
(integer) 1

127.0.0.1:6379> GET stat
"1"

In Python:

>>> con.set("count",1);
True

>>> con.incr("count");
2

>>> con.get("count");
'2'

In python redis library, you’ll get the following exception when you try to increment a key that has string value.

>>> con.incr("site");
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "build/bdist.linux-x86_64/egg/redis/client.py", line 915, in incr
  File "build/bdist.linux-x86_64/egg/redis/client.py", line 573, in execute_command
  File "build/bdist.linux-x86_64/egg/redis/client.py", line 585, in parse_response
  File "build/bdist.linux-x86_64/egg/redis/connection.py", line 582, in read_response
redis.exceptions.ResponseError: value is not an integer or out of range
>>> con.get("site");
'thegeekstuff'

14. INCRBY: Increase the Value by Given Increment

Instead of incrementing the number by 1, you can increatement it by any given number using INCRBY command as shown below.

In the following example, we are incrementing the key “count” by 3.

127.0.0.1:6379> SET count 5
OK

127.0.0.1:6379> INCRBY count 3
(integer) 8

127.0.0.1:6379> GET count
"8"

Note: Just like INCR, when you try INCRBY on a key that doesn’t exist, it will create that key, set the value to 0, and then do the increment as shown below.

127.0.0.1:6379> GET statistics
(nil)

127.0.0.1:6379> INCRBY statistics 5
(integer) 5

127.0.0.1:6379> GET statistics
"5"

In Python:

>>> con.set("count",1);
True

>>> con.incrby("count",3);
4

>>> con.get("count");
'4'

Note: In python redis library, we can also use incr command itself to increment it by any value as shown below.

>>> con.set("count",1);
True

>>> con.incr("count",3);
4

15. DECR: Decrease the Value by One

This is similar to INCR, but DECR will decrease the value by one as shown below.

127.0.0.1:6379> SET count 5
OK

127.0.0.1:6379> DECR count
(integer) 4

In Python:

>>> con.set("count",10);
True

>>> con.decr("count")
9

16. DECRBY: Decrease the Value by Given Decrement

This is similar to INCRBY, but DECRBY will decrease the value by the given number as shown below.

127.0.0.1:6379> SET count 5
OK

127.0.0.1:6379> DECRBY count 2
(integer) 3

In Python, we have incrby function, but there is no decrby function. However, we can use the decr function itself, but pass the value to be decremented as parameter:

>>> con.get("count");
'10'

>>> con.decr("count",3);
7

17. INCRBYFLOAT: Increase the Float Value by Given Increment (Fraction Values)

You can increment a number with a float value (number with decimal point values) using the INCRBYFLOAT function as shown below.

127.0.0.1:6379> SET price 93.5
OK

127.0.0.1:6379> GET price
"93.5"

127.0.0.1:6379> INCRBYFLOAT price 0.3
"93.8"

This works even when the key contains an integer value and not float value as shown below.

127.0.0.1:6379> SET count 3
OK

127.0.0.1:6379> INCRBYFLOAT count 0.3
"3.3"

If you don’t specify a value to increment by, you’ll get the following error message:

127.0.0.1:6379> INCRBYFLOAT price
(error) ERR wrong number of arguments for 'incrbyfloat' command

When you try to use INCRBYFLOAT on a string value, you’ll get the following error message.

127.0.0.1:6379> INCRBYFLOAT site 0.3
(error) ERR value is not a valid float

127.0.0.1:6379> GET site
"thegeekstuff"

In Python:

>>> con.set("price",93.5);
True

>>> con.incrbyfloat("price",0.3);
93.799999999999997

In python, the last parameter is opitional, if you don’t specify a value, it will be incremented by 1.0 as shown below.

>>> con.set("count",3);
True

>>> con.incrbyfloat("count");
4.0

18. MSET: Set Multiple Keys and Values

MSET is similar to SET command, but this can set multiple key/value pair using one command as shown below.

127.0.0.1:6379> MSET site "thegeekstuff" blog "TGS" forum "The Geek Stuff"
OK

127.0.0.1:6379> GET site
"thegeekstuff"

127.0.0.1:6379> GET blog
"TGS"

127.0.0.1:6379> GET forum
"The Geek Stuff"

In Python, you first have to define a dict mapping as shown below. “sites” is a dict mapping which has three key-values.

>>> sites = {"site":"thegeekstuff", "blog":"TGS", "forum":"The Geek Stuff"}

Next, set the above “sites” dict using mset as shown below.

>>> con.mset(sites);
True

Verify:

>>> con.get("site")
'thegeekstuff'

>>> con.get("blog")
'TGS'

>>> con.get("forum")
'The Geek Stuff'

19. MGET: Retrieve Values from Multiple Keys

MGET is similar to GET command, but this can retrive and display values of multiple keys using one command as shown below.

127.0.0.1:6379> MGET site blog forum
1) "thegeekstuff"
2) "TGS"
3) "The Geek Stuff"

In Python:

>>> con.mget("site","blog","forum");
['thegeekstuff', 'TGS', 'The Geek Stuff']

20. MSETNX: Set Value ONLY When ALL Keys Don’t Exist

This is a combination of SETNX and MSET command. This will set the values for the given keys only when ALL of them don’t already exist. This will not perform any of the assignment even if one of the key already exists.

For example, the following will set the values for the three keys (site, author and email) only when ALL three of them don’t exists earlier.

In our case, the key “site” already exists. So, this will not set the value for all three of these keys.

127.0.0.1:6379> MSETNX site "The Geek Stuff" author "Ramesh Natarajan" email "ramesh@thegeekstuff.com" 
(integer) 0

As you see below, the site key still has old value, and author and email are not defined.

127.0.0.1:6379> MGET site author email
1) "thegeekstuff"
2) (nil)
3) (nil)

But, if we delete the “site” key and try again, MSETMX will work and set the values for all the three keys as shown below.

127.0.0.1:6379> DEL site
(integer) 1

127.0.0.1:6379> MSETNX site "The Geek Stuff" author "Ramesh Natarajan" email "ramesh@thegeekstuff.com" 
(integer) 1

127.0.0.1:6379> MGET site author email
1) "The Geek Stuff"
2) "Ramesh Natarajan"
3) "ramesh@thegeekstuff.com"

In Python, define a dict mapping that contains multiple key/value pair, and use that as a parameter to msetnx as shown below:

>>> myargs = {"site":"The Geek Stuff", "author":"Ramesh Natarajan", "email":"ramesh@thegeekstuff.com"}

>>> con.msetnx(myargs);
False

>>> con.mget("site","author","email");
['thegeekstuff', None, None]