Diff output from two programs without temporary files
Use <(command) to pass one command's output to another program as if it were a file name. Bash pipes the program's output to a pipe and passes a file name like /dev/fd/63 to the outer command.
diff <(./a) <(./b)Similarly you can use >(command) if you want to pipe something into a command.
This is called "Process Substitution" in Bash's man page.
One option would be to use named pipes (FIFOs):
mkfifo a_fifo b_fifo./a > a_fifo &./b > b_fifo &diff a_fifo b_fifo... but John Kugelman's solution is much cleaner.