I'm doing some foundational review to make sure I'm on solid footing when I'm working on Rails – currently going through Software Carpentry's Unix shell for novices sequence – and there is this wee thing I think I never knew.

In a Unix shell,

cd -

will take you back to the previous directory.

How I could not know this after half my life in IT?  I'm going to posit that it doesn't exist in DOS,  and I just plain missed it when I made the transition because I could get wherever I needed to be easily.

As you were.