shl(1)                                                     shl(1)



NAME
     shl - manages the layering of multiple shells

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
     keyboard are blocked.  Output from multiple layers is
     multiplexed onto the terminal.

     The stty character swtch (set to CONTROL-z if NULL) is used
     to switch control to shl from a layer.  The shl program 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 and ioctl.
     Each layer has its own process group ID.

        Note:  Only one instance of shell layering may be
        invoked 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
     significant.  The names (1) through (7) cannot be used when
     creating 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]
          Creates a layer called name and makes 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]...
          Blocks the output of the corresponding layer when it is
          not the current layer, for each name.



January 1992                                                    1

shl(1)                                                     shl(1)



     delete name [name]...
          Deletes the corresponding layer for each name.  All
          processes in the process group of the layer are sent
          the SIGHUP signal (see signal(3)).

     help(or?)
          Prints the syntax of the shl commands.

     layers [-l][name]...
          Lists the layer name and its process group for each
          name.  The -l option produces a ps(1)-like listing.  If
          no arguments are given, information is presented for
          all existing layers.

     resume [name]
          (followed by RETURN).  Makes 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).  Resumes the layer that was
          current before the last current layer.

     unblock name [name]...
          Does not block the output of the corresponding layer
          when it is not the current layer, for each name.

     quit Exits shl.  All layers are sent the SIGHUP signal.

     name (followed by RETURN).  Makes the layer referenced by
          name the current layer.

FILES
     /usr/bin/shl
          Executable file
     /dev/sxt/???
          Virtual tty device files
     $SHELL
          Variable file containing pathname of the shell to use
          (default is /bin/sh).

SEE ALSO
     sh(1), stty(1),

     ioctl(2), signal(3), sxt(7) in A/UX Programmer's Reference

     A/UX Shells and Shell Programming








2                                                    January 1992