commandloop ?prompt1? ?prompt2?
              Create  an interactive command loop for the current
              TCL interpreter.  This  command  receives  commands
              from  stdin  and  executes  them.  It is useful TCL
              scripts that do not normally converse interactively
              with  a user through a Tcl command interpreter, but
              which sometimes want to enter this mode.

              Prompt1 is a Tcl command  that is evaluated to out-
              put  a prompt string.  The old value of tcl_prompt1
              is saved and it is set to this value for the  dura-
              tion  of  the  command  loop.  Prompt2 is a command
              that  is  evaluated  to  output   the   ``downlevel
              prompt'',  which  is the prompt which is issued for
              continuation input.  The old value  of  tcl_prompt2
              is  saved and it is set to this value for the dura-
              tion of the command loop.

              When the command terminates, the variables for  the
              prompt  hooks  will  be set to their old value.  If
              these arguments are not specified, the prompt hooks
              use their current value.

              This command is provided by Extended Tcl.