Earlier quoted context omitted.
GNU sleep is around 150 loc, and does significantly less...
GNU programs are not a reference. They must have usage(), and handle --help and --version. Even /bin/true. coreutils-8.25$ wc -l src/true.c 80 src/true.c
Ding has `--version`, and a help message too :P
To be honest, a big chunk of it is just handling user input and attempting to provide useful error messages.