shl, the shell layer manager

shl can run multiple shells in parallel on a single terminal. It was
originally introduced in AT&T's SVr3 Unix, but discontinued by most
vendors later since csh-style job control was considered superior.
This free implementation avoids most of the complications by using
regular SVR4-style pseudo terminals; it can be used together with
job control. The user-visible differences to the original shl are:

	* The layer terminal devices are /dev/pts/* instead of
	  /dev/sxt/*.

	* The stty loblk and stty -loblk commands have no effect;
	  there is no way to block output from within a layer.

	* Blocking a layer will stop its output from appearing on
	  the user's terminal, but programs within the layer will
	  continue to write() until the pseudo terminal's buffers
	  are filled.

With these exceptions, this implementation should conform to the
description given in shl(AU_CMD) of the System V Interface Definition,
Third Edition. It also contains some SCO and HP-UX extensions.

shl has been tested on:

	Solaris		8, 2.6
	UnixWare	7.1.1, 2.1
	Linux		2.6, 2.4 with glibc 2.2, 2.3

It should run on most SVR4-like systems; please contact me to extend
this list and send a diff if necessary.

Gunnar Ritter							2/21/04