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Given a shell script (bash in this example), one can use the set -x or -x passed to bash or other supporting shells to generate debug output.
I know how to redirect said output to a file ./script.sh 2> out.log or bash -x script.sh 2> out.log.
But how to send stderr to a terminal multiplexer, like screen or tmux?
Mainly useful when script change the way the terminal is displayed(TUI), so sending stderr enable more comfortable debugging in another window/terminal.
Invoke tty in the terminal you want to send something to. It will print e.g. /dev/pts/3 Then redirect anything you want to this file, possibly from another terminal. Like this:
bash -x script.sh 2> /dev/pts/3
This works with tmux, screen, separate terminal emulators or ttys (where you are logged in). Invoke tty in one shell and redirect/print to whatever it says from the other.
I use similar approach to debug my pipelines. Example:
foo | tee /dev/pts2 | filter1 | tee /dev/pts3 | filter2
tmux command display '#{pane_tty}' will print /dev/pts/3 or so in the status line. This is useful if there's no shell in the target pane (so you cannot easily run tty there). Select the pane so it's current, hit prefix:, type the command and Enter.
cat /dev/pts/3 in a loop, inside a tmux/screen session? (need to continuously see the debug output)
Oct 31, 2020 at 20:25
ps ax | grep $$ | awk '{ print $2 }' inside the wanted pane in tmux, and then pipe to it like in your example. (feel free to add this method to your answer too)
Oct 31, 2020 at 20:29
cat. Spawn two terminals, two shells; it doesn't matter if with tmux, screen, separate terminal emulators or ttys. Invoke tty in one and redirect/print to whatever it says from the other.
Oct 31, 2020 at 20:29