Useful built-in macOS command-line utilities

open -n file.pdf : opens new instance of Preview application which is useful if you want to open the same file twice (for example to look at different pages at once).

caffeinate -d : prevents display turning off, useful if you want to look at display without moving mouse.

Not mine (found online years ago), but here's the opposite. `cd` into the frontmost Finder window:

  cd "$(osascript -e 'tell app "Finder" to POSIX path of (insertion location as alias)')";