Preserve bash history across multiple sessions

Copying & pasting long command lines across open terminal sessions feels so wrong. Specially since Ctrl-R could find that hairy one-liner after just a few keystrokes. Except it is buffered in another session. Fortunately, bash is flexible enough to commit every command to the history immediately:

export HISTCONTROL=ignoreboth:erasedups # no duplicate entries
export HISTSIZE=100000                  # big big history
export HISTFILESIZE=100000              # big big history
shopt -s histappend                     # append to history, don't overwrite it

# Save and reload the history after each command finishes
export PROMPT_COMMAND="history -a; history -c; history -r; $PROMPT_COMMAND"

Discovered at Preserve bash history in multiple terminal windows.