I have an app that launches an authentication helper (my script) and uses STDIN/STDOUT to communicate. I want to re-direct STDIN and STDOUT from this script to two named pipes for interaction with another program. E.g.: SCRIPT_STDIN pipe1 SCRIPT_STDOUT < pipe2 Here is the flow I'm trying to accomplish: [Application] - Launches helper script, writes to helpers STDIN, reads from helpers STDOUT (example: STDIN:username,password; STDOUT:LOGIN_OK) [Helper Script] - Reads STDIN (data from app), forwards to PIPE1; reads from PIPE2, writes that back to the app on STDOUT [Other Process] - Reads from PIPE1 input, processes and returns results to PIPE2 The cat command can almost do what I want. If there were an option to copy STDIN to STDERR I could make cat do this with a command (assuming the fictitious option -e echos to STDERR rather than STDOUT): cat -e PIPE2 2PIPE1 (read from PIPE2 and write it to STDOUT, copy input, normally going to STDERR to PIPE1)