In this section, we'll use the common grep search utility on your (UNIX-like) OS to do the searching for you when your program is called with the previously added -f flag.
Your task is to "shell out" the search string to the grep utility to do the search rather than rely on your own string-searching logic.
Use https://gobyexample.com/spawning-processes as a guide for this exercise.
https://gobyexample.com/execing-processes
https://gobyexample.com/signals
When your program shuts down, users (sysadmins, etc) will expect it to behave like any other UNIX/Linux utility. Hence, you will want to exit cleanly and perform as expected when you application receives OS signals like SIGINT, SIGHUP and others.
Example: https://gobyexample.com/exit
Most Go applications can use os.Exit(code int) or something that implicitly calls on os.Exit like log.Fatal.
ProTip: Avoid using os.Exit or code that calls on os.Exit during unit tests. The test run will simply exit and short-circuit.