tee coprocess vs tee pipe in Korn shell I had this piece of code which logged the output of a while loop to a file but also showed it on the screen: while ... do ... done | tee logfile A code change required to set a variable in the while loop and make it known after the loop had ended so I tried while ... do x=123 ... done | tee logfile echo x=$x but x was empty since in a piped sequence the while loop is considered to be a sub shell and thus it cannot set variables in the parent process. There is a solution though in Korn shell using coprocesses . # Start a coprocess to log input to logfile via tee # and report it also to the current tty (tee logfile >/dev/tty) |& # Send output of while loop to coprocess while ... do x=123 ... done >&p echo x=$x will report x correctly. This works fine for my example where the script is run always in a terminal window. If the script is run in the background or via cron its (terminal) output needs to be captured, anything else...