watch:tldr:918d7

The command "watch" is used in Unix-like operating systems to periodically execute another command and display its output on the terminal.

In this case, the command consists of a pipeline where three commands, command_1, command_2, and command_3 are executed in sequence with their output being passed to the next command using the pipe symbol (|).

The use of backticks (${}) indicates that the commands within them are variables, so instead of literally executing "${command_1} | ${command_2} | ${command_3}", the values of those variables will be substituted in.

So when the command is executed, it will periodically execute command_1, then pass its output as input to command_2, and finally pass the output of command_2 as input to command_3. The output of the whole pipeline will be displayed on the terminal. The frequency at which the commands are executed is determined by the watch command.