how do i pass a plsql exit code to a shell variable?

Question

My code traps various exit codes for various conditions and stores the value to a local variable; I'm then passing it to a bind var which I am using to store the exit code. My code is something like:

variable errflag number
   begin
      variable vflag number;
         if
           cond 1
           then
              vflag:=1;
             .
             .
             .
             .
              .
          elsif
            cond n
               then
                 vflag:=n;
               else
                 ...do nothing..
              end if;
              :errflag:=vflag;
end;
/
             exit :errflag

but I am getting the below error after running

SP2-0670: Internal number conversion failed Usage: { EXIT | QUIT } [ SUCCESS | FAILURE | WARNING | n | | : ] [ COMMIT | ROLLBACK ]

any ideas??? :\