mtr:tldr:50527

The command "mtr -4 ${host}" is used to run the "mtr" command with a specific option and value passed as arguments. Here's an explanation of each part:

1. "mtr": It is a network diagnostic tool that combines the functionality of traceroute and ping. The "mtr" command stands for "My traceroute".

2. "-4": It is an option flag used with the "mtr" command. In this case, the "-4" flag specifies that the command should use IPv4 only and not IPv6. It forces the "mtr" tool to use IPv4 addresses for network diagnostic tests like traceroute.

3. "${host}": It is a placeholder for a variable value that should be provided when running the command. The actual hostname or IP address of the target host should be substituted in place of "${host}". For example, if the target host is "example.com", the command will be executed as "mtr -4 example.com".

Overall, this command will execute the "mtr" tool using IPv4 addresses only and target the specified host or IP address for network diagnostic purposes.