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 keyboard are blocked.  Output from multiple layers is multiplexed 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 <undef>) 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 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 ]
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 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. 

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. 

ADDED VALUE

This entry, supplied by INTERACTIVE Systems Corporation, contains enhancements to UNIX System V. 
 

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