memcached 命令行

## Starting memcached

### 默认端口 11211， 如果想要改变端口，用-p

```
memcached -p 8000
memcached -d -p 8000
```

### 如何判断memcached已经启动过了

```
ps aux | grep memcached
```

### 退出memcached

```
quit
```

### 终止memcached service

```
brew install pidof
pidof memcached
```
```
kill -9
```

```
memcached -p 11111 -U 11111 -u user -d
-p is for TCP port number
-U is for UDP port number
-u is for user name
-d runs memcached as daemon process
```

## Connect to memcached

```
# 连接 memcached
telnet 127.0.0.1 11211
```

## Storage Commands
### Set Data
Memcached set command is used to set a value to key; if the key does not exist, a new key is created and value is assigned to that key.

`set key flags exptime bytes`

- key - It is the name of the unique key by which data is accessed.
- flags - It is the 32-bit unsigned integer that the server stores with the data provided by the user, and returns along with the data when the item is retrieved.
- exptime - It is the expiration time (seconds) of data stored in cache. A 0 value means "never expire". If the exptime is more than 30 days then Memcached interprets it as UNIX timestamp for expiration.
- bytes - This is the length of the data in bytes that needs to be stored in Memcached.
- value - It is the data that needs to be stored. The data needs to be given on the new line after executing the command with the above options.

```
// bytes 要和value的character数目完全一样
set bittiger 0 900 9
memcached

get bittiger
```

### Add Data
Memcached `add` command is used to set a value to a new key. If the key already exists, then it gives the output NOT_STORED.

```
add key flags exptime bytes
value
```

### Replace Data
Memcached `replace` command is used to replace the value of an existing key.

```
replace key flags exptime bytes

```

### Append/Prepend
Memcached `append/prepend` command is used to add data in an existing key. This data is added at the `start/end` of the previous value.

```
append key flags exptime bytes
```

### CAS (Check-And-Set)
Memcached CAS command 'checks' and 'set' data item if and only if, no other client process has updated it since last read by this client. The `unique_cas_token` is obtained from the `gets` command.
[Reference](https://www.tutorialspoint.com/memcached/memcached_cas.htm)

```
cas key flags exptime bytes unique_cas_token
```

## Retrieval Commands
### Get
```
get key1 key2 key3
```
### Gets
Memcached gets command is used to get the value with CAS token.

```
gets key1 key2 key3
```

### Delete
```
delete key
```

### Incr/Decr
略

## Statistics Commands

The issue contains memcached command-line and storage/retrieval notes but names no repository file, test, or documentation entry point. First locate where project documentation is maintained; done would require placing this material in the appropriate location and verifying that its commands and explanations are accurate and complete.

Written by the indexing model from the issue text.