Use dtach + script + cat to make a "pick up where I left off" session management tool

sessionize.bash

#!/bin/bash

USAGE="sessionize: Build a disconnection-tolerant interactive session

Usage: sessionize [session_name] [command ...]

With no arguments, lists active sessions

If session_name is specified, either create or attach to it and run $SHELL as
an interactive login shell.

If session_name and command are specified, create the session and run command.

Uses dtach for session management, and script + cat to try and bring you back
to where you left off.

This is experimental and might suck.

If you don't like the \"rely on a race condition to keep your replayed session
from getting cleared by dtach\" thing, I have a patched dtach that adds a -C
option to stop it from doing that, it's here:

https://github.com/njvack/dtach

Note that by setting SESSIONIZE_STATE_DIR and changing permissions on your
session socket (and its parent directories), you can have multiple people
connect to one session -- so if you want to share a terminal, that should
work. Note that you'll want to have the two terminals at the same size or
things will look weird.

I'm not sure if you can just make the new session non-writeable if you only
want them to see what you're doing.
"

if [ -n "${SESSIONIZE_NAME+x}" ]; then
  echo "You're already in a session called ${SESSIONIZE_NAME}"
  exit 1
fi

ARGS=("$@")

shopt -sq nullglob

SESSIONIZE_STATE_DIR="${SESSIONIZE_STATE_DIR:-/tmp/$USER/dtach}"

# No arguments, list the active sessions
if [[ $# -eq 0 ]]; then
  sockets=("$SESSIONIZE_STATE_DIR"/*sock)
  if [[ ${#sockets[@]} == 0 ]]; then
    echo "No active sessions."
    echo
    echo "sessionize -h for help"
    exit 0
  fi

  echo "Active sessions:"
  for sock in "${sockets[@]}"; do
    base="$(basename "$sock")"
    sesname="${base%.*}"
    echo "$sesname"
  done
  echo
  echo "sessionize -h for help"
  exit 0
fi

if [[ $# -eq 1 && ("$1" == "-h" || "$1" == "--help") ]]; then
  printf "%s\n" "${USAGE}" | fmt -w "$(tput cols)"
  exit
fi

export SESSIONIZE_NAME="$1"

mkdir -p "${SESSIONIZE_STATE_DIR}"
chmod 700 "${SESSIONIZE_STATE_DIR}"

export SESSIONIZE_LOG="${SESSIONIZE_STATE_DIR}/${SESSIONIZE_NAME}.log"
export SESSIONIZE_DTACH_SOCKET="${SESSIONIZE_STATE_DIR}/${SESSIONIZE_NAME}.sock"

if [ ${#ARGS[@]} -lt 2 ]; then
  CMD=("$SHELL -i -l")
else
  CMD=("${ARGS[@]:1}")
fi

if [ -S "${SESSIONIZE_DTACH_SOCKET}" ]; then
  # Spawn a background subshell that waits 0.1 second and then replays the
  # saved session.
  # This kind of gross but gets around dtach clearing the screen after attaching
  # (sleep 0.1 && cat "${SESSIONIZE_LOG}") &
  # dtach -a "$SESSIONIZE_DTACH_SOCKET" -z -r winch
  #
  # Alternative approach: Use dd to eat the 6-byte "clear" VT100 escape code
  # It's not racey but it does leave you in `cat`
  # Maybe this is better? It's definitely more fun.
  cat "${SESSIONIZE_LOG}"
  dtach -a "$SESSIONIZE_DTACH_SOCKET" -z -r winch | (
    dd bs=6 count=1 status=none of=/dev/null
    cat
  )
else
  dtach -c "$SESSIONIZE_DTACH_SOCKET" -z -r winch script -q -f -e -c "${CMD[@]}" "$SESSIONIZE_LOG"
fi