SHL(1)               INTERACTIVE UNIX System               SHL(1)



          NAME
               shl - shell layer manager

          SYNOPSIS
               shl

          DESCRIPTION
               The shl command 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.  To have the output of a layer
               blocked when it is not current, the stty option loblk may be
               set within the layer.

               The stty character swtch (set to ^Z if NUL) 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 manipulated
               like a real tty device using stty(1) and ioctl(2).  Each
               layer has its own process group id.

             Definitions
               A name is a sequence of characters delimited by a blank,
               tab, or new-line.  Only the first eight characters are sig-
               nificant.  The names (1) through (7) cannot be used when
               creating a layer.  They are used by shl when no name is sup-
               plied.  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
                    created with a name of the form (#) where # is the last
                    digit 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.  This is
                    equivalent to setting the stty option -loblk within the
                    layer.
               delete name [ name ... ]
                    For each name, delete the corresponding layer.  All


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          SHL(1)               INTERACTIVE UNIX System               SHL(1)



                    processes in the process group of the layer are sent
                    the SIGHUP signal [see signal(2)].
               help (or ?)
                    Print the syntax of the shl commands.



















































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               layers [ -l ] [ name ... ]
                    For each name, list the layer name and its process
                    group.  The -l option produces a ps(1)-like listing.
                    If no arguments are given, information is presented for
                    all existing layers.
               resume [ name ]
                    Make the layer referenced by name the current layer.
                    If no argument is given, the last existing current
                    layer will be resumed.
               toggle
                    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.
                    This is equivalent to setting the stty option -loblk
                    within the layer.
               quit Exit shl.  All layers are sent the SIGHUP signal.
               name Make the layer referenced by name the current layer.

          FILES
               /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), sxt(7).
               ioctl(2), signal(2) in the INTERACTIVE SDS Guide and
               Programmer's Reference Manual.


























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