tmux-smartsplit.sh

#!/bin/bash
# tmux-smartsplit
# open a new tmux (split-)window which will automatically
# continue the existing ssh session if one exists

SIP=$(tmux display-message -p "#S:#I:#P")
PTY=$(tmux server-info |
        egrep flags=\|bytes |
        awk '/windows/ { s = $2 }
             /references/ { i = $1 }
             /bytes/ { print s i $1 $2 } ' |
        grep "$SIP" |
        cut -d: -f4)
PTS=${PTY#/dev/}
PID=$(ps h -eao pid,tty,command --forest | awk '$2 == "'$PTS'" {print $1; exit}')

CHILD=$(cat /proc/[0-9]*/stat | awk '$4 == '$PID' {print $1; exit}')

NEW_WIN_CMD=""
if [[ "$CHILD" != "" ]]; then
	NEW_WIN_CMD=$(python3.3 -c 'import shlex, sys; parts = list(filter(None, open(sys.argv[1]).read().split("\0"))); print(" ".join(map(shlex.quote, parts)) if parts[0] == "ssh" else "")' "/proc/$CHILD/cmdline")
fi

case "$1" in
	h)
		tmux splitw -h "$NEW_WIN_CMD"
		;;
	v)
		tmux splitw -v "$NEW_WIN_CMD"
		;;
	*)
		tmux neww "$NEW_WIN_CMD"
		;;
esac

tmux.conf

bind '"' run-shell -b 'tmux-smartsplit v'
bind % run-shell -b 'tmux-smartsplit h'