How I live without shell job control

September 25, 2016

In my comments on yesterday's entry, I mentioned that my shell doesn't support job control. At this point people who've only used modern Unix shells might manage how you get along without such a core tool as job control. The answer, at least for me, is surprisingly easily (at least most of the time).

Job control is broadly useful for three things: forcing programs to pause (and then un-pausing them), pushing programs into the background to get your shell back, and calling backgrounded programs back into the foreground. In other words, job control is one part suspending and restarting programs and one part multiplexing a single session between multiple programs.

It's possible that I'm missing important uses of being able to easily pause and unpause programs. However, I'm not missing the ability in general, because you can usually use SIGSTOP and SIGCONT by hand. I sometimes wind up doing this, although it's not something I feel the need for very often.

(I do sometimes Ctrl-C large makes if I want to do something else with my machine; with job control it's possible that I'd suspect the make instead and then have it resume afterwards.)

My approach to the 'recover my shell' issue is to start another shell. That's what windows are for (and screen), and I have a pretty well developed set of tools to make new shells cheap and easy; in my opinion, multiple windows are the best and most flexible form of multiplexing. I do sometimes preemptively clone a new window before I run a command in the foreground, and I'll admit that there are occasions when I start something without backgrounding it when I really should have done otherwise. A classical case is running 'emacs file' (or some other GUI program) for what I initially think is going to be a quick use and then realizing that I want to keep that emacs running while getting my shell back.

(This is where my habit of using vim in a terminal is relevant, since that takes over the terminal anyways. I can't gracefully multiplex such a terminal between, say, vim and make; I really want two terminals no matter what.)

So far I can't think of any occasions where I've stuck a command into the background and then wanted it to be in the foreground instead. I tend not to put things in the background very much to start with, and when I do they're things like GNU Emacs or GUI programs that I can already interact with in other ways. Perhaps I'm missing something, but in general I feel that my environment is pretty good at multiplexing things outside of job control.

(At the same time, if someone added job control to my shell of choice, I wouldn't turn my nose up at it. It just seems rather unlikely at this point, and I'm not interested in switching shells to get job control.)

Sidebar: multiplexing and context

One of the things that I like about using separate windows instead of multiplexing several things through one shell is that separate windows clearly preserve and display the context for each separate thing I'm doing. I don't have to rebuild my memory of what a command is doing (and what I'm doing with it) when I foreground it again; that context is right there, and stays right there even if I wind up doing multiple commands instead of just one.

(Screen sessions are somewhat less good at this than terminal windows, because scrollback is generally more awkward. Context usually doesn't fit in a single screen.)

PS: the context is not necessarily just in what's displayed, it's also in things like my history of commands. With separate windows, each shell's command history is independent and so is for a single context; I don't have commands from multiple contexts mingled together. But I'm starting to get into waving my hands a lot, so I'll stop here.


Comments on this page:

By mtk@acm.org at 2016-09-27 19:50:55:

job control predates unix, think tops20 or maybe even multics? tops20 for sure, though. it was the way to manage multiple processes when there was one terminal, period. and of course, that terminal was physical.

Written on 25 September 2016.
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