TMUX split and duplicate your current SSH session

tmux-split-ssh.sh

#!/usr/bin/env bash

usage() {
  echo "Usage: $(basename "$0") ARGS"
  echo
  echo "Arguments:"
  echo "  -v|-h       Vertical or horizontal split"
  echo "  --fail      Error out if there is no SSH session in the current pane"
  echo "  --verbose   Display a message when spawning a new SSH session/pane"
  echo "  --no-shell  Don't spawn a shell after the SSH command"
  echo "  -c DIR      Set start directory for pane"
}

get_current_pane_info() {
  tmux display -p '#{pane_id} #{pane_pid}'
}

get_current_pane_id() {
  get_current_pane_info | awk '{ print $1 }'
}

get_pane_pid_from_pane_id() {
  tmux list-panes -F "#{pane_id} #{pane_pid}" | awk "/^$1 / { print \$2}"
}

# $1 is optional, disable 2120
# shellcheck disable=2120
get_ssh_command() {
  local pane_id
  local pane_pid

  pane_id="${1:-$(get_current_pane_id)}"
  pane_pid="$(get_pane_pid_from_pane_id "$pane_id")"

  if [[ -z "$pane_pid" ]]
  then
    echo "Could not determine pane PID" >&2
    return 3
  fi

  for child_pid in $(pgrep -P "${pane_pid}")
  do
    child_cmd="$(ps -o cmd= "$child_pid")"
    if [[ "$child_cmd" =~ ^(auto)?ssh.* ]]
    then
      echo "$child_cmd"
      return
    fi
  done
  return 1
}

if [[ "${BASH_SOURCE[0]}" == "${0}" ]]
then

  SPLIT_ARGS=()

  while [[ -n "$*" ]]
  do
    case "$1" in
      help|h|--help)
        usage
        exit 0
        ;;
      -h|-v)
        SPLIT_ARGS+=("$1")
        shift
        ;;
      -c)
        if [[ -z "$2" ]]
        then
          echo "Missing start directory" >&2
          usage >&2
          exit 2
        fi
        SPLIT_ARGS+=(-c "$2")
        shift 2
        ;;
      --fail)
        FAIL=1
        shift
        ;;
      --no-shell|-n)
        NO_SHELL=1
        shift
        ;;
      --verbose|-V)
        VERBOSE=1
        shift
        ;;
      -*)
        usage >&2
        exit 2
        ;;
    esac
  done

  ssh_command="$(get_ssh_command)"

  if [[ -z "$ssh_command" ]]
  then
    if [[ -n "$FAIL" ]]
    then
      tmux display "Error: current pane seems to not be running SSH..."
      echo "Could not determine SSH command" >&2
    else
      tmux split "${SPLIT_ARGS[@]}"
    fi
    exit 0
  fi

  start_cmd="$ssh_command"

  if [[ -z "$NO_SHELL" ]]
  then
    default_shell="$(tmux show-option -gqv "default-shell")"

    if [[ -z "$default_shell" ]]
    then
      # Fall back to sh
      default_shell="$(command -v sh)"
    fi

    # Append default shell
    start_cmd+="; ${default_shell}"
  fi

  if [[ -n "$VERBOSE" ]]
  then
    start_cmd="echo '🧙👉 Running \"$ssh_command\"'; $start_cmd"
  fi

  # Spawn a new shell after the ssh command to keep the pane alive
  tmux split "${SPLIT_ARGS[@]}" "$start_cmd"
fi

# vim: set ft=bash et ts=2 sw=2 :

tmux.conf

# Prefix-S: SSH split
unbind S
bind S run "$TMUX_BIN_HOME/tmux-split-ssh.sh -c #{pane_current_path} --verbose -v"

# Prefix-|: SSH split (horizontal)
unbind |
bind | run "$TMUX_BIN_HOME/tmux-split-ssh.sh -c #{pane_current_path} --verbose -h"

This is now a tmux plugin: https://github.com/pschmitt/tmux-ssh-split