I love learning new unix commands because there is infinite ways to become more productive. When you work alongside some unix power user wizards like I do I frequently retrace through the
history to analyze how they did something. At the moment, my new favorite is
watch. A basic example I've used a few times already is:
watch 'ls -la | grep somefile.txt'
By default this will refresh a file list every 2 seconds. It has other cool options I need to explore like changing the refresh time and highlighting changes in a new color. Super useful when you're monitoring for something.
Apparently you can install this on Mac OS X via Homebrew
brew install watch.