The main "clock$\_$display" program compiled from C is designed to read times from stdin and display them as above. To make a complete clock, a "shell script" called clock.sh must print the times to be displayed by the clock executable. In other words, the compiled C program doesn't do any timekeeping itself: it only displays values received from some other source, while the shell script just prints times in a boring old format that can be read by the C program