       commandloop  ?-async?  ?-interactive  on|off|tty?
              ?-prompt1 cmd? ?-prompt2 cmd? ?-endcommand cmd?
              Create an interactive command loop reading commands
              from stdin and writing results to stdout.   Command
              loops  are  maybe  either be blocking or event ori-
              ented.  This command is useful for Tcl scripts that
              do  not normally converse interactively with a user
              through a Tcl command interpreter, but which  some-
              times  want  to enter this mode, perhaps for debug-
              ging or user configuration.  The command loop  ter-
              minates 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 com-
                   mand is available.  That command will then  be
                   evaluated.   An event loop must be entered for
                   input to be read and processed.

            -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 emu-
                   lator.  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 dif-
                   ference 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)
                   command prompt.  If not specified, the command
                   in tcl_prompt2  is  evaluated  to  output  the
                   prompt.

            -endcommand cmd
                   If  specified,  cmd is evaluated when the com-
                   mand 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.
