HISTCONTROL
A colon-separated list of values controlling how commands are saved on the history list.
If the list of values includes ignorespace, lines which begin with a space character
are not saved in the history list. A value of ignoredups causes lines matching the
previous history entry to not be saved. A value of ignoreboth is shorthand for
ignorespace and ignoredups. A value of erasedups causes all previous lines matching
the current line to be removed from the history list before that line is saved.
Any value not in the above list is ignored. If HISTCONTROL is unset, or does not
include a valid value, all lines read by the shell parser are saved on the history
list, subject to the value of HISTIGNORE. The second and subsequent lines of a
multi-line compound command are not tested, and are added to the history regardless
of the value of HISTCONTROL.
