Practical combat: Let’s talk about the list command in Redis through sample code

This article will introduce you to the list command in Redis, and learn how to use the list command through code examples. I hope it will be helpful to you!

The data structure of list

The List type is a double-ended linked list structure with a capacity of 2 The 32nd power minus 1 element, that is, more than 4 billion; its main functions include push, pop, getting elements, etc.; it is generally used in stacks, queues, message queues and other scenarios. [Related recommendations: Redis video tutorial]

Redis list command practice

[l/r]push-left /Add elements to the right

Syntax: [l/r]push key value [value ...]

Insert with head or tail Insert one or more elements into the specified key queue

127.0.0.1:6379> lpush pushkey 1 2 3
(integer) 3
127.0.0.1:6379> lpush pushkey 4
(integer) 4
127.0.0.1:6379> rpush pushkey 5
(integer) 5
127.0.0.1:6379> lrange pushkey 0 -1
1) "4"
2) "3"
3) "2"
4) "1"
5) "5"

lrange-query range element

Syntax: lrange key start stop

Get elements within the specified range of the list

127.0.0.1:6379> lpush products 1 2 3
(integer) 3
127.0.0.1:6379> lpush products 4 5 6
(integer) 6
127.0.0.1:6379> lrange products 0 -1
1) "6"
2) "5"
3) "4"
4) "3"
5) "2"
6) "1"

linsert-Insert elements before and after an element

Syntax ：linsert key BEFORE|AFTER pivot value

Insert elements before or after the elements in the list

127.0.0.1:6379> lrange products 0 -1
1) "6"
2) "5"
3) "4"
4) "3"
5) "2"
6) "1"
127.0.0.1:6379> linsert products before 5 a
(integer) 7
127.0.0.1:6379> lrange products 0 -1
1) "6"
2) "a"
3) "5"
4) "4"
5) "3"
6) "2"
7) "1"
127.0.0.1:6379> linsert products after a b
(integer) 8
127.0.0.1:6379> lrange products 0 -1
1) "6"
2) "a"
3) "b"
4) "5"
5) "4"
6) "3"
7) "2"
8) "1"

llen-get the length

Syntax: llen key

Get the length of the list

127.0.0.1:6379> lrange products 0 -1
1) "6"
2) "a"
3) "b"
4) "5"
5) "4"
6) "3"
7) "2"
8) "1"
127.0.0.1:6379> llen products
(integer) 8

lindex-Get the element based on the subscript

Syntax: lindex key index

Get the elements in the list by index

127.0.0.1:6379> lrange products 0 -1
1) "6"
2) "a"
3) "b"
4) "5"
5) "4"
6) "3"
7) "2"
8) "1"
127.0.0.1:6379> lindex products 2
"b"

lset-According to the following Index setting value

Syntax:lset key index value

Set the value of the list element by index

127.0.0.1:6379> lrange products 0 -1
1) "6"
2) "a"
3) "b"
4) "5"
5) "4"
6) "3"
7) "2"
8) "1"
127.0.0.1:6379> lset products 2 B
OK
127.0.0.1:6379> lrange products 0 -1
1) "6"
2) "a"
3) "B"
4) "5"
5) "4"
6) "3"
7) "2"
8) "1"

ltrim-Intercept elements

Syntax: ltrim key start end

Intercept the elements in the specified range of the queue, and delete the remaining elements

127.0.0.1:6379> lrange products 0 -1
1) "6"
2) "a"
3) "B"
4) "5"
5) "4"
6) "3"
7) "2"
8) "1"
127.0.0.1:6379> ltrim products 0 3
OK
127.0.0.1:6379> lrange products 0 -1
1) "6"
2) "a"
3) "B"
4) "5"

lrem-Remove elements

Syntax: lrem key count value

Remove list elements

127.0.0.1:6379> lpush test a 1 a 2 a 3 a 4  5 6
(integer) 10
127.0.0.1:6379> lrange  test 0 -1
 1) "6"
 2) "5"
 3) "4"
 4) "a"
 5) "3"
 6) "a"
 7) "2"
 8) "a"
 9) "1"
10) "a"
127.0.0.1:6379> lrem test 3 a
(integer) 4
127.0.0.1:6379> lrange  test 0 -1
1) "6"
2) "5"
3) "4"
4) "3"
5) "2"
6) "1"
7) "a"

[l/r]pop-pop element from left/right

##Syntax:

[l/r]pop key

Pop a node element from the head or tail of the queue (return the element and delete it from the queue)

127.0.0.1:6379> lrange  test 0 -1
1) "6"
2) "5"
3) "4"
4) "3"
5) "2"
6) "1"
127.0.0.1:6379> lpop test
"6"
127.0.0.1:6379> lrange  test 0 -1
1) "5"
2) "4"
3) "3"
4) "2"
5) "1"
127.0.0.1:6379> rpop test
"1"
127.0.0.1:6379> lrange  test 0 -1
1) "5"
2) "4"
3) "3"
4) "2"

rpoplpush-remove the right element and add it to another A list left

Syntax:

rpoplpush source destination

Removes the last element (right) of the list and adds that element to the other A list (left) and returns

127.0.0.1:6379> lpush src 1 2 3
(integer) 3
127.0.0.1:6379> lrange src 0 -1
1) "3"
2) "2"
3) "1"
127.0.0.1:6379> lpush dst a b c
(integer) 3
127.0.0.1:6379> lrange dst 0 -1
1) "c"
2) "b"
3) "a"
127.0.0.1:6379> rpoplpush src dst
"1"
127.0.0.1:6379> lrange src 0 -1
1) "3"
2) "2"
127.0.0.1:6379> lrange dst 0 -1
1) "1"
2) "c"
3) "b"
4) "a"

b[l/r]pop-blocks popping one element left/right

Syntax:

b[l/r]pop key1 [key2 ...] timeout

Remove and get the first or last element of the list, if there are no elements in the list, it will

block the listUntil the wait times out or finds a pop-up element.

127.0.0.1:6379> lpush list1 1 2
(integer) 2
127.0.0.1:6379> lpush list2 a b
(integer) 2
127.0.0.1:6379> lrange list1 0 -1
1) "2"
2) "1"
127.0.0.1:6379> lrange list2 0 -1
1) "b"
2) "a"
127.0.0.1:6379> blpop list1 list2 10
1) "list1"   #弹出元素所属的列表
2) "2"       #弹出元素所属的值
127.0.0.1:6379> blpop list1 list2 10
1) "list1"
2) "1"
127.0.0.1:6379> blpop list1 list2 10
1) "list2"
2) "b"
127.0.0.1:6379> blpop list1 list2 10
1) "list2"
2) "a"
127.0.0.1:6379> blpop list1 list2 10
(nil)
(10.08s)  # 列表为空的时候，就等待超时10秒

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