ol -- Option Line

               default range             syntax
                 1,$                      ol[$ | . | # | BLANK]

        The  "l"  option  is the Line number monitoring option. Typing
        "l" followed by "$" constantly displays the last  line  number
        in the file (current length of the file).  Typing "l" followed
        by  "."   constantly  displays  the current line number.  This
        usually make sense only in conjunction with the  "oa"  option,
        that uses letters for line names.

        For general information about the option command, type "ho".
        See also:  "hoa" and "hequal".