<li> Investigate the <code>parse_for_user()</code> function, with the <code>usage_data_file</code>. <b>In main, call `parse_for_user()` with `output` as the argument. Investigate what's returned.</b>
<li> <code>parse_for_user()</code> should take the list of lines from the file, and instead return a list of usernames. <b>In main, print the title header and the output. Commit the change.</b>
<li> <b>Once you have `output` --> `parse_for_user()` --> correct output being printed, use if conditions to print only when `-l user` is in the command line arguments.</
<li> <b>Continue committing these changes as your proceed.</b>
<li> Implement the same things as parse_for_user but for <code>parse_for_hosts</code>. Use the user function to guide you.