I've had this in my .bashrc for years. I thought it came from this post judging from my commments, but looks different, so I wonder whether it came from HN comments when this was previously posted.

  ## Better bash history
  # Avoid duplicates
  export HISTCONTROL=ignoredups:erasedups
  # When the shell exits, append to the history file instead of overwriting it
  shopt -s histappend
  # After each command, append to the history file and reread it
  export PROMPT_COMMAND="${PROMPT_COMMAND:+$PROMPT_COMMAND$'\n'}history -a; history -c; history -r"