commandloop ?-async? ?-interactive on | off

          Create an interactive  command  loop  reading  commands
          from  stdin  and  writing  results  to stdout.  Command
          loops are maybe either be blocking or  event  oriented.
          This command is useful for Tcl scripts that do not nor-
          mally converse interactively with a user through a  Tcl
          command  interpreter, but which sometimes want to enter
          this mode, perhaps for debugging or user configuration.
          The command loop terminates on EOF.

          The following options are available:

          -async
               A command handler will be associated  with  stdin.
               When  input is available on stdin, it will be read
               and accumulated until a full command is available.
               That  command  will  then  be evaluated.  An event
               loop must be entered for input to be read and pro-
               cessed.

          -interactive on | off | tty
               Enable or disable interactive  command  mode.   In
               interactive  mode,  commands  are prompted for and
               the results of comments are  printed.   The  value
               maybe  any  boolean value or tty.  If tty is used,
               interactive mode is enabled if stdin is associated
               with a terminal or terminal emulator.  The default
               is tty.

          -prompt1 cmd
               If specified, cmd  is used  is  evaluate  and  its
               result  used  for the main command prompt.  If not
               specified, the command in tcl_prompt1 is evaluated
               to  output  the  prompt.   Note  the difference in
               behavior, cmd results is used,  while  tcl_prompt1
               outputs.  This is to allow for future expansion to
               command loops that write to other than stdout.

          -prompt2 cmd
               If specified, cmd is  used  is  evaluate  and  its
               result  used for the secondary (continuation) com-
               mand prompt.  If not  specified,  the  command  in
               tcl_prompt2 is evaluated to output the prompt.

          -endcommand cmd
               If specified, cmd is evaluated  when  the  command
               loop terminates.

               In interactive mode, the results of  set  commands
               with two arguments are not printed.
               If SIGINT is configured to generate a  Tcl  error,
               it can be used to delete the current command being
               type without aborting the program in progress.

     This command is provided by Extended Tcl.