Nobody knows this: the bash extension <(cmd) to pass the output of a command, as if it was a file, to another command. Example to diff the list of files in 2 directories (a and b) without using temporary files:

  $ diff -u <(cd a && find . | sort) <(cd b && find . | sort)

Internally, bash creates a pipe and passes /dev/fd/XXX to the main command.