       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
                     command 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 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 (continua-
                     tion) command prompt.  If not specified, the
                     command  in tcl_prompt2 is evaluated to out-
                     put the prompt.

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

                     In interactive mode, the results of set com-
                     mands 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 pro-
                     gram in progress.
