The following snippet should work on every system that has coreutils.
$ shuf /usr/share/dict/words --repeat --random-source /dev/random -n 5
You can swap /usr/share/dict/words with any good word list, like EFF’s or Arnold Reinhold’s Diceware list.
You can also add it to your ~/.bash_aliases for ease of use:
alias passphrase="shuf ~/dotfiles/misc/diceware8k.txt --repeat --random-source /dev/random -n"
Then you can easily use it in bash:
$ passphrase 5
notch
kane
to
drag
cater