I have read the
history command help page and tried both of the options(
r). As far as I understand, both options ensure that the history file is read and valid in the current shell, so it does the same thing. I wonder what makes it different?
-n Append the history lines not already read from the history file to the current history list. These are lines appended to the history file since the beginning of the current Bash session. -r Read the current history file and append its contents to the history list.