       hash name path
              Puts name in the command hash table, associating it
              with the pathname path.  Whenever name is used as a
              command argument, the shell will try to execute the
              file given by path.

       unhash [ -m ] name ...
              The  entry  in  the command hash table, if any, for
              each name is removed. If the -m flag is  given  the
              arguments  are taken as patterns (should be quoted)
              and all entries for commands  with  matching  names
              will be removed.
