ZooKeeper provides a very simple command-line client, zkCli, under the bin directory of the ZooKeeper installation directory.

[root@s1 zk]# ls /usr/local/zookeeper/bin/
zkCleanup.sh  zkCli.sh  zkEnv.sh  zkServer.sh

First connect to a ZooKeeper instance that has been started. For example:

zkCli.sh -server localhost:2181

A lot of information will be output during the connection. When the connection is successful, it will enter ZooKeeper's interactive mode:

WatchedEvent state:SyncConnected type:None path:null

[zk: localhost:2181(CONNECTED) 0]   # Enter the commands allowed by ZooKeeper here

For example, input help and output help information.

[zk: localhost:2181(CONNECTED) 0] help
ZooKeeper -server host:port cmd args
        stat path [watch]
        set path data [version]
        ls path [watch]
        delquota [-n|-b] path
        ls2 path [watch]
        setAcl path acl
        setquota -n|-b val path
        history 
        redo cmdno
        printwatches on|off
        delete path [version]
        sync path
        listquota path
        rmr path
        get path [watch]
        create [-s] [-e] path data acl
        addauth scheme auth
        quit 
        getAcl path
        close 
        connect host:port
[zk: localhost:2181(CONNECTED) 1] 

There is an increasing number in the interactive command prompt, for example, when the above operation is performed sequentially, it changes from 0 to 1. This number represents the historical number of the command.

You can also use the non-interactive mode of zkCli.sh to perform one-time operations in the following format:

zkCli.sh -server IP:PORT COMMAND

For example, the help command:

zkCli.sh -server localhost:2181 help

ZooKeeper's commands are rarely simple and can be roughly divided into several types:

1. create: create a node somewhere in the tree.
   
2. delete: delete a node.
   
3. Exists: Test whether a node exists.
   
4. get data: Read node data.
   
5. set data: Write data to a node.
   
6. get children: Retrieve a list of child nodes of a node.
   
7. sync: Waiting for data to be propagated.

Note that this is only the functional type of commands, and does not mean that they are commands.

For example, create a znode node:

[zk: localhost:2181(CONNECTED) 1] create /zk_test mydata1
Created /zk_test

Where / zk_test is the node name and mydata1 is the data carried by the node.

Create a child node:

[zk: localhost:2181(CONNECTED) 2] create /zk_test/child_node1 "mydata2"
Created /zk_test/child_node1

View the child nodes under a node. Note that there is no recursive retrieval.

[zk: localhost:2181(CONNECTED) 3] ls /
[zookeeper, zk_test]

[zk: localhost:2181(CONNECTED) 4] ls /zk_test
[child_node1]

Get node data, status information:

[zk: localhost:2181(CONNECTED) 6] get /zk_test
mydata1
cZxid = 0x4
ctime = Wed Jun 27 02:05:44 CST 2018
mZxid = 0x4
mtime = Wed Jun 27 02:05:44 CST 2018
pZxid = 0x5
cversion = 1
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 7
numChildren = 1

[zk: localhost:2181(CONNECTED) 7] get /zk_test/child_node1
mydata2
cZxid = 0x5
ctime = Wed Jun 27 02:29:12 CST 2018
mZxid = 0x5
mtime = Wed Jun 27 02:29:12 CST 2018
pZxid = 0x5
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 7
numChildren = 0

If you just want to get the status information of the node, you can use the stat command:

[zk: localhost:2181(CONNECTED) 8] stat /zk_test
cZxid = 0x4
ctime = Wed Jun 27 02:05:44 CST 2018
mZxid = 0x4
mtime = Wed Jun 27 02:05:44 CST 2018
pZxid = 0x5
cversion = 1
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 7
numChildren = 1

The ls2 command can obtain the child nodes under a given node and the state information of the given node:

[zk: localhost:2181(CONNECTED) 12] ls2 /
[zookeeper, zk_test]    # List of child nodes
cZxid = 0x0
ctime = Thu Jan 01 08:00:00 CST 1970
mZxid = 0x0
mtime = Thu Jan 01 08:00:00 CST 1970
pZxid = 0x4
cversion = 0
dataVersion = 0
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 0
numChildren = 2      # Number of child nodes

The set command is used to modify the node:

[zk: localhost:2181(CONNECTED) 13] set /zk_test "mydata2"
cZxid = 0x4
ctime = Wed Jun 27 02:05:44 CST 2018
mZxid = 0x9
mtime = Wed Jun 27 02:42:45 CST 2018
pZxid = 0x7
cversion = 2
dataVersion = 1
aclVersion = 0
ephemeralOwner = 0x0
dataLength = 7
numChildren = 0

Delete can delete nodes. Note that it will not be deleted recursively, so to delete a node containing a child node, you need to delete all the child nodes first.

[zk: localhost:2181(CONNECTED) 21] delete /zk_test
Node not empty: /zk_test

[zk: localhost:2181(CONNECTED) 22] delete /zk_test/child_node1

The history command lists 10 command histories of recent operations and gives the number of each historical command. The redo commands can be re-invoked based on the number of historical commands.

[zk: localhost:2181(CONNECTED) 18] history
8 - stat /zk_test
9 - get /
10 - get child /
11 - get children /
12 - ls2 /
13 - ls /
14 - ls2 /zk_test
15 - get /
16 - help
17 - ls /zk
18 - history

Re-execute the historical order No. 13:

[zk: localhost:2181(CONNECTED) 27] redo 13
[zookeeper, zk_test]

quit command exits ZooKeeper's interactive command line.

[zk: localhost:2181(CONNECTED) 29] quit
Quitting...