lpr
The BSD Unix command that hands a file to the print queue — the client half of the lpd spooler.
It arrived with 4.2BSD in the early 1980s as part of Berkeley's line-printer system. lpr file.ps queues a job, lpq shows the queue and lprm cancels one. The command talks to lpd, the line printer daemon, which owns the spool directory and feeds the printer. The wire protocol itself was only standardised after the fact as RFC 1179 (1990) — TCP port 515, a spare design with no authentication at all. lpr/lpd ruled Unix printing for two decades until CUPS and IPP displaced them in the 2000s, yet the command name survives as an alias long after the daemon beneath it was swapped out.