shl(1)                                                     shl(1)



     NAME
          shl - shell layer manager

     SYNOPSIS
          shl

     DESCRIPTION
          shl allows a user to interact with more than one shell from
          a single terminal.  The user controls these shells, known as
          layers, using the commands described below.

          The current layer is the layer which can receive input from
          the keyboard.  Other layers attempting to read from the key-
          board are blocked.  Output from multiple layers is multi-
          plexed onto the terminal.

          The stty character swtch (set to CONTROL-z if NULL) is used
          to switch control to shl from a layer.  shl has its own
          prompt, >>>, to help distinguish it from a layer.

          A layer is a shell which has been bound to a virtual tty
          device (/dev/sxt/???).  The virtual device can be manipulat-
          ed like a real tty device using stty(1) and ioctl(2).  Each
          layer has its own process group ID.

             Note:  Only one instance of shell layering may be in-
             voked in any given login session.


        Definitions
          A name is a sequence of characters delimited by a blank, tab
          or newline.  Only the first eight characters are signifi-
          cant.  The names (1) through (7) cannot be used when creat-
          ing a layer.  They are used by shl when no name is supplied.
          They may be abbreviated to just the digit.

        Commands
          The following commands may be issued from the shl prompt
          level.  Any unique prefix is accepted.

          create [name]
               Create a layer called name and make it the current
               layer.  If no argument is given, a layer will be creat-
               ed with a name of the form (#) where # is the last di-
               git of the virtual device bound to the layer.  The
               shell prompt variable PS1 is set to the name of the
               layer followed by a space.  A maximum of seven layers
               can be created.
          block name [name ...]
               For each name, block the output of the corresponding
               layer when it is not the current layer.
          delete name [name ...]



     April, 1990                                                     1

     shl(1)                                                     shl(1)



               For each name, delete the corresponding layer.  All
               processes in the process group of the layer are sent
               the SIGHUP signal (see signal(3)).
          help (or ?)
               Print the syntax of the shl commands.
          layers [-l] [name ...]
               For each name, list the layer name and its process
               group.  The -l flag option produces a ps(1)-like list-
               ing.  If no arguments are given, information is
               presented for all existing layers.
          resume [name]
               (followed by RETURN).  Make the layer referenced by
               name the current layer.  If no argument is given, the
               last existing current layer will be resumed.
          toggle
               (followed by RETURN).  Resume the layer that was
               current before the last current layer.
          unblock name [name ...]
               For each name, do not block the output of the
               corresponding layer when it is not the current layer.
          quit Exit shl.  All layers are sent the SIGHUP signal.
          name (followed by RETURN).  Make the layer referenced by
               name the current layer.

     FILES
          /usr/bin/shl
          /dev/sxt/???      Virtual tty devices
          $SHELL            Variable containing path name of the shell
                            to use (default is /bin/sh).

     SEE ALSO
          sh(1), stty(1), ioctl(2), signal(3), sxt(7).
          A/UX User Interface.






















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