The legacy program, provided by CUPS for sending files to the printer queues on the command line is:

lpd is the Line Printer Daemon, which is the server process that manages print queues, not the command for sending jobs.

lpp is not a standard command for printing or managing print queues.

lpq is used to view the status of printer queues and print jobs, not to send jobs.

lpr (line printer remote) is the standard command-line utility derived from the original BSD printing system, which CUPS reimplements for submitting files to a print spool. When CUPS is installed, lpr acts as an interface to the CUPS system to add jobs to the print queue.