NIS Adduser scripts
One of the most important in the computer field is to know what computers are good at, and what computers are not so good at. Anything that involves repeating a fixed or mostly fixed set of steps is something that computers are very good at. At one of my jobs, adding users to the NIS database had been done by hand - copying and pasting lines between files. I automated this process with a script that worked for both shadowed and non-shadowed passwd files, and was much easier to use. I also made a varient on it that allowed for the restting of a user's password (instead of having to copy the password hash between files).