Bash: read stdin from file and write stdout to file

Question

I\'m trying to run an app (let\'s say top) so it will read from a file for stdin and write to another file from stdout.

Currently I have

Answer 1

Let's forget about top, that appears to be a red herring.

To map stdin or stdout to files, you can use redirection:

some_program < input_file          # Redirects stdin

another_program > output_file      # Redirects stdout

or even:

yet_another  < input_file > output_file

Answer 2

Is there a way I can map stdin and stdout to files and use them to control a cli app?

It sounds like you are looking for coprocesses, added to Bash in 4.0.

coproc cat                    # Start cat in background
echo Hello >&${COPROC[1]}     # Say "Hello" to cat
read LINE <&${COPROC[0]}      # Read response
echo $LINE                    # cat replied "Hello"!

Before 4.0 you had to use two named pipes to achieve this.