My dotfiles[1,2] are full of various functions to do stuff. Half of them I jacked from other people[3] when I was using Bash and ported to ZSH when I discovered Oh-my-zsh. However, a few are my own. The ones that I did write are often one-liners that take an argument and pass it to a series of commands that I'd rather not type. For example history | grep -i command, ls -lah | grep dir, or my favorite, cd dir; ls. If I have to do any logic, aside from determining what OS I'm on, I look to python.
[1] https://github.com/yramagicman/dotfiles [2] https://github.com/yramagicman/zsh-aliases [3] https://github.com/mathiasbynens/dotfiles/blob/master/.funct...