Final answer:
The correct command to print a file is 'lpr', which sends the file to the printer's queue in Unix-based systems. 'print' and 'ptr' are not standard commands for this task.
Step-by-step explanation:
The command used to print a file in Unix-based systems is lpr. When you want to print a document from the command line, you can use this command followed by the filename. It sends the file to the printer's queue. Neither print nor ptr are standard Unix or Linux commands for printing files. The lpr command is part of the Common Unix Printing System (CUPS), which is used for managing printers and print requests on most Unix-like operating systems.