nginx:hosts:list

This command involves piping the output of one command to the input of another command in order to filter and display specific information.

Explanation:

1. nginx is the command to manage the NGINX web server.
2. The -T option is used to test the configuration files for syntax errors and prints the parsed configuration to the standard output.
3. | is a pipe symbol used to redirect the output of the previous command (nginx -T) to the input of the next command (grep server_name).
4. grep is a command-line utility used to search for specific patterns in a text.
5. server_name is the pattern that grep will search for in the input provided.

Overall, this command will execute the nginx -T command to fetch the server configuration and then the output will be filtered using grep to display only the lines containing the text "server_name". This can be useful to quickly identify the server names configured in NGINX.