Install vi command in docker container

1. When using the docker container, sometimes there is no vim installed in it. When you type the vim command, the prompt says: vim: command  not  found, you need to install vim at this time, but when you type the apt-get install vim command, it prompts:  
2. Reading package lists... Done  
3. Building dependency tree         
4. Reading state information... Done  
5. E: Unable to locate package vim  
6. At this time, you need to type: apt-get  update . The function of this command is to synchronize the indexes of the sources listed in /etc/apt/sources.list and /etc/apt/sources.list.d, so that the latest version can be obtained. package.  
7. After the update is complete, type the command: apt-get install vim command.