BASH one-line if
I recently learned about this:
(( 1 )) && echo "true" || echo "false"
Which is a great way to do an if statement on a single line, if you ask me. I could just do if [[ cond ]]; do something else; another thing; fi but I think this one is pretty slick.
[[ cond ]] && <what happens if true> || <what happens if false>