String type common operations for redis data type operations

redis 127.0.0.1:6379> set name "zhangshan" //Assign key name zhangshan
OK
redis 127.0.0.1:6379> get name
"zhangshan"

getrange String interception
redis 127.0.0.1:6379> getrange name 0 3 //Intercept the substring of 0-3
"zhan"

getset sets the new value and returns the old value
redis 127.0.0.1:6379> getset name "wangwu" //Assign the specified key and return the previous value
"zhangshan"
redis 127.0.0.1:6379> get name //Check the value of name and it becomes wamgwu
"wangwu"

setex sets the key value and sets the expiration time
redis 127.0.0.1:6379> setex name 30 "zbb" //Set the value of the key whose key is name to zbb, and set the expiration time to 3 seconds
OK
redis 127.0.0.1:6379> get name
"zbb"
redis 127.0.0.1:6379> ttl name //Expire after 13 seconds left
(integer) 13

strlen gets the length of a string value.
redis 127.0.0.1:6379> set name "zbbbbb"
OK
redis 127.0.0.1:6379> strlen name //Get the length of the string value stored by key as name
(integer) 6

mset sets multiple key-value pairs at the same time
redis 127.0.0.1:6379> mset key1 "c++" key2 "c#" key3 "java" key4 "node.js"
OK
redis 127.0.0.1:6379> get key1
"c++"
redis 127.0.0.1:6379> get key2
"c#"
redis 127.0.0.1:6379> get key3
"java"
redis 127.0.0.1:6379> get key4
"node.js"

append appends a string
redis 127.0.0.1:6379> set zbb_key  "ku bi cheng xu yuan !"
OK
redis 127.0.0.1:6379> append zbb_key "yes we all" //Append "yes we all" to the string stored in key zbb_key
(integer) 29
redis 127.0.0.1:6379> get zbb_key //Check the result again, it has been added
"ku bi cheng xu yuan ! yes we all"
redis 127.0.0.1:6379>