Bash configuration for shared history:

  # Append to ~/.bash_history instead of overwriting it -- this stops terminals
  # from overwriting one another's histories.
  shopt -s histappend
  # Only load the last 1000 lines from your ~/.bash_history -- if you need an
  # older entry, just grep that file.
  HISTSIZE=1000
  # Don't truncate ~/.bash_history -- keep all your history, ever.
  unset HISTFILESIZE
  # Add a timestamp to each history entry.
  HISTTIMEFORMAT="%Y/%m/%d %H:%M:%S  "
  # Don't remember trivial 1- and 2-letter commands.
  HISTIGNORE=?:??
  # What it says.
  HISTCONTROL=ignoredups
  # Save each history entry immediately (protects against terminal crashes/
  # disconnections, and interleaves commands from multiple terminals in correct
  # chronological order).
  PROMPT_COMMAND="history -a; $PROMPT_COMMAND"