Split stderr from comand to separate tmux pane

spliterr.sh

#!/bin/bash
set -m

showhelp() {
    echo "Usage: $0 [-ohvrc] <command>"
    echo "Pipes stderr from command to a new tmux pane."
    echo "  -h | -v     split horizontally or vertically (default vertically)"
    echo "  -r          send stdout to pane instead of stderr"
    echo "  -o          send both stdout and stderr to new panes"
    echo "  -c          close pane automatically after program terminates"
    exit 1
}

direction=-v
revdir=-h
reverse=
splitout=
close=
while true; do
    case $1 in 
        -h)
            direction=-v
            revdir=-h
            ;;
        -v)
            direction=-h
            revdir=-v
            ;;
        -r)
            reverse=1;; 
        -o)
            splitout=1;;
        -c)
            close=1;;
        -*|"")
            showhelp;;
        *)
            break;;
    esac
    shift
done

pipeerr=1
if [ -n "$splitout" ]; then
    pipeout=1
fi
if [ -n "$reverse" ]; then
    pipeerr="$pipeout"
    pipeout=1
fi

thedate() { 
    date '+%y/%m/%d %H:%M:%S' 
}

mkpipe() {
    { pipe=$(mktemp) && 
        rm -f "$pipe" && 
        mkfifo "$pipe" &&
        echo "$pipe"
    } || {
        echo "failed creating named pipe";
        exit 1
    }
}

err=/dev/stderr
out=/dev/stdout

if [ -n "$pipeout" ]; then
    out=$(mkpipe)
fi
if [ -n "$pipeerr" ]; then
    err=$(mkpipe)
fi

"$@" > "$out" 2> "$err" &

pid=$!
if [ -n "$pipeout" ]; then 
    outpane=$(tmux split-window $direction -PdI -F "#D" "echo -ne '\e[37m'; echo '[$(thedate) stdout for $pid:' $* ']'; echo -ne '\e[0m'; cat $out; echo -e '\e[37m'; read")
    target="-t $outpane"
    direction=$revdir
fi
[[ -n "$pipeerr" ]] && errpane=$(tmux split-window $direction $target -PdI -F "#D" "echo -ne '\e[37m'; echo '[$(thedate) stderr for $pid:' $* ']'; echo -ne '\e[0m'; cat $err; echo -e '\e[37m'; read")

fg %1 >/dev/null
exitcode=$?

message="[$(thedate) Process terminated (exit code $exitcode), press Enter to close]"
[[ -n "$close" ]] && message="C-m"
[[ -n "$pipeout" ]] && tmux send-keys -t "$outpane" "$message"
[[ -n "$pipeerr" ]] && tmux send-keys -t "$errpane" "$message"

rm -f pipe