emulate [ -R ] {zsh|sh|ksh|csh}
       Set up zsh options to emulate the  specified  shell
       as  much as possible.  csh will never be fully emu-
       lated.  If the argument is not one  of  the  shells
       listed  above,  zsh  will be used as a default.  If
       the -R option is given, all options  are  reset  to
       their  default value corresponding to the specified
       emulation mode.
