Append to ~/.bash_history "immediately"
Bash normally waits until a session (terminal) is closed before it writes commands to the history.
You can add a call to
history -a to
PROMPT_COMMAND to make bash to append your history to
~/.bash_history every time it displays your prompt.
PROMPT_COMMAND="history -a; $PROMPT_COMMAND"
The environment variable
PROMPT_COMMAND is executed when bash is about to display your prompt.
history -a appends the current history to