Bash tip: Default value for a variable

In my Bash scripts, I used to hack my way around default values for variables. Turns out there is a very simple way to give your variables a default value while also letting other override them if they want to:

FOO=${BAR-bar}

If someone export's BAR, then FOO will equals the already exported value of $BAR, if $BAR doesn't exist then FOO will have the value of the literal 'bar'.