Redis List Data Structure

Redis lists are string-based collections that maintain insertion order. Elements can be added to either the head (left) or tail (right) of a list. A Redis list can hold up to 2^32 - 1 elements, enabling storage of more than 4 billion items per list.

Getting Help for List Commands

You can use the following command to view list-related operations:

127.0.0.1:6379> help @list

Creating Lists

Inserting Elements from the Left

Use LPUSH to add one or more elements to the left of the list:

127.0.0.1:6379> LPUSH mylist ddfff 21 nb
(integer) 3
127.0.0.1:6379> LRANGE mylist 0 -1
1) "nb"
2) "21"
3) "ddfff"

Appending Elements to the Right

Use RPUSH to add one or more elements to the right of the list:

127.0.0.1:6379> RPUSH mylist qq ll nn
(integer) 6
127.0.0.1:6379> LRANGE mylist 0 -1
1) "nb"
2) "21"
3) "ddfff"
4) "qq"
5) "ll"
6) "nn"

Prepending Elements Only If List Exists

LPUSHX adds elements to the left only if the list already exists:

127.0.0.1:6379> LPUSHX mylist ww ee
(integer) 8
127.0.0.1:6379> LPUSHX youlist ww ee
(integer) 0

Appending Elements Only If List Exists

RPUSHX appends elements to the right only if the list exists:

127.0.0.1:6379> RPUSHX mylist rr nn
(integer) 10
127.0.0.1:6379> RPUSHX youlist rr nn
(integer) 0

Inserting Elements Before or After a Pivot

Use LINSERT to insert an element before or after a specific value:

127.0.0.1:6379> LINSERT mylist before ddfff www
(integer) 8
127.0.0.1:6379> LINSERT mylist after ddfff eee
(integer) 9

Removing Elements

Removing Elements by Value

LREM removes a specified number of occurrences from the list, starting from the left:

127.0.0.1:6379> LREM mylist 2 we
(integer) 2

Modifying Elements

Setting a Value at a Specific Index

Use LSET to update the value at a specific position:

127.0.0.1:6379> LSET mylist 1 clearlove7

Trimming Lists

Keeping Only a Range of Elements

LRANGE shows elements within a specified range, and LRANGE combined with LRANGE can be used to verify the result:

127.0.0.1:6379> LTRIM mylist 1 4

Querying Lists

Retrieving a Range of Elements

127.0.0.1:6379> LRANGE mylist 0 -1

Getting an Element by Index

127.0.0.1:6379> LINDEX mylist 0

Getting the Length of a List

127.0.0.1:6379> LLEN mylist

Removing and Returning Elements

• From the left: LPOP
• From the right: RPOP

Moving Elements Between Lists

RPOPLPUSH removes the last element from one list and pushes it to another:

127.0.0.1:6379> RPOPLPUSH mylist testlist

Blocking Pop Operations

Blocking Pop from the Left

BLPOP blocks until an element becomes available in the list:

# Client A
127.0.0.1:6379> BLPOP testlist 100

# Client B
127.0.0.1:6379> LPUSH testlist we

# Client A
127.0.0.1:6379> BLPOP testlist 100
1) "testlist"
2) "we"