job control in Sys V - (nf)

[jab at uokvax.UUCP]

#R:sri-arpa:-82700:uokvax:6100034:004:1637
uokvax!jab    Jun 18 19:43:00 1984

/***** uokvax:net.unix / sri-arpa!ARPA / 10:11 pm  Jun 14, 1984 */
From:  Preston Mullen <mullen at NRL-CSS.ARPA>

I keep seeing hints that System V (perhaps only release 2?)
has some form of job control.  Could someone elaborate on this
and compare it with 4.2bsd job control?  I am especially
interested in job control at the user command (shell) level,
not capabilities that are only implemented in system calls.
/* ---------- */

I'll tell you about it, with a quick disclaimer: I'll provide you with facts
(not a rave about how good it is, or a flame about how bad it is) and let
you for your own opinions.

System V Release 2.0 has a utility called "shell layers", named after
the "layers" program that runs on the Teletype 5620 terminal and implements
windows on the dot-mapped-display screen.

"shell layers" is best thought of as a "virtual terminal" facility, although
it isn't as complete as the Purdue "pseudo-tty" driver. You are given the
ability to run up to seven virtual terminals (each with its own /dev entry),
and switch between them via a magic character, which is usually ^Z.

For example,

	% shl
	>>> create layer1
	layer1				(PS1 is set to the layer name)
	layer1 ls
		(output from ls)
	layer1 ^Z
	>>> create layer2
	layer2 cd /
	layer2 ^Z
	>>> resume layer1
	(resuming layer1)
	layer1

You get the gist. The magic differences from the "job control" you see now
is that ^Z takes you to a "manager", not to a shell, and that the programs
in each "virtual terminal" don't know that they're running in a layer.

Let's not get into a discussion on whether this is a good or bad implementation.

	Jeff Bowles
	Lisle, IL