shl(C)

Syntax

Description

The current layer is the layer that 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(C) option loblk may be set within the layer.

The stty character swtch (set to <Ctrl>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 that has been bound to a virtual tty device (/dev/sxt??[0-7] or /dev/sxt/??[0-7]). The virtual device can be manipulated like a real tty device using stty and ioctl(S). Each layer has its own process group ID.

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

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, or, if super user, the name followed by a sharp (#) and 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(S)).

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(C)-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.

Limitations

shl normally accesses sxt??? devices correctly at all times. Other programs may be able to work with these devices if they have the correct protocol and device name; however some programs may not expect devices to be located outside /dev, and some programs may expect all terminal devices to begin with the prefix tty.

If shl does not run properly on a particular terminal, you may have to set istrip for that terminal's line by entering the following command at the terminal:

stty istrip

By default, the Operating System is not configured for shell layers. To add this to kernel, use the command:

mkdev shl

This executes a script which prompts you for the number of sessions desired. The script also allows you to relink the kernel. The new session limit becomes effective after the kernel is rebooted. (For more information, see mkdev(ADM).)

Files

/dev/sxt??[0-7] or

/dev/sxt/??[0-7]

virtual tty devices

$SHELL

variable containing pathname of the shell to use (default is /bin/sh)

See also

Standards conformance

AT&T SVID Issue 2.