TUHS

tuhs@tuhs.org

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6536 discussions

Were cron and at done at the same time? Or one before the other?

by M Douglas McIlroy

This pair of commands exemplifies a weakness in the way Unix evolved. Although it was the product of a shared vision, It was not a product-oriented project. Unix commands work well together, but they don't necessarily work alike. It would be nice if identifiable families of commands had similar user interfaces. However, cron and at were written by different individuals, apparently with somewhat different tastes. Unix folks were close colleagues, but had no organized design committee. Time specs in cron and at are markedly different. A more consequential example is data-field specs (or lack thereof) in sort, join, cut, comm and uniq. The various specs were recognized as "wildly incongruent" in a BUG remak. However there was no impetus for unification. To paraphrase John Cocke (speaking about Fortran): one must understand that Unix commands are not a logical language. They are a natural language--in the sense that they developed by organic evolution, not "intelligent design". Doug

4 years, 7 months

sh and goto

by srbourne

Message: 4 Date: Mon, 30 Nov 2020 19:59:18 -0800 (PST) From:jason-tuhs@shalott.net To:tuhs@minnie.tuhs.org Subject: Re: [TUHS] The UNIX Command Language (1976) Message-ID: <alpine.LRH.2.23.453.2011301946410.14253(a)waffle.shalott.net> Content-Type: text/plain; charset="utf-8"; Format="flowed" > "The UNIX Command Language is the first-ever paper published on the Unix > shell. It was written by Ken Thompson in 1976." > > https://github.com/susam/tucl Thanks for that. This reminded me that the Thompson shell used goto for flow control, which I had forgotten. Bourne commented on the omission of goto from the Bourne shell, "I eliminated goto in favour of flow control primitives like if and for. This was also considered rather radical departure from the existing practice." Was this decision contentious at all? Was there a specific reason for goto's exclusion in the Bourne shell? Thanks. -Jason At the time it may have raised a few eyebrows but I don't recall much discussion about it then. My email tracks at the time don't mention it. Doug McIlroy or Steve Johnson (or Ken) on this forum might recall differently. At the time scripts were not that complicated and so error recovery to a far off place in the script was not common. As an aside I did persuade Dennis to add "setjmp" and "longjmp" so the shell code itself could recover from some kinds of script errors. So I did not have a "religious" aversion to "goto" at the time. Steve

4 years, 7 months

sh and goto

by M Douglas McIlroy

> Bourne commented on the omission of goto from the Bourne shell ... > Was this decision contentious at all? Was there a specific reason for goto's exclusion in the Bourne shell? I don't believe I ever used a shell goto, because I knew how it worked--maybe even spinning a tape drive, not too different from running a loop on the IBM CPC. There you stood in front of the program "read head" (a card reader), grabbed the "used" cards at the bottom and put them back in the top feed. Voila, a program loop. The shell goto differed in that it returned to the beginning by running the tape backward rather than going around a physically looped path. And you didn't have to spin the tape by hand. It also reminds me of George Stibitz's patent on the goto. The idea there was to stop reading this tape and read that one instead. The system library was a bank of tape readers with programs at the ready on tape loops . (This was in the late 1940s. I saw the machine but never used it. I did have hands-on experience with CPCcards.) Doug

4 years, 7 months

Knuth and Pascal (was "Were cron and at ...")

by M Douglas McIlroy

Off topic, but too much fun to pass up. >> You wrote your algorithm in Pascal, debugged it, and then rewrote it in your favourite language (in my case, ALGOL-W). > Now why didn't Don Knuth think of that for TeX? I'm glad he didn't. He might have written it in Mix. Knuth once said he didn't believe in higher-level languages. Of course he knew more about them than anybody else and was CACM's associate editor for the subject--like a minister who doesn't believe in God. Doug

4 years, 7 months

Re: [TUHS] Were cron and at done at the same time? Or one before the other?

by jnc＠mercury.lcs.mit.edu

> From: "Theodore Y. Ts'o" > Having a clean architecture is useful in so far as it makes reduces > maintenance overhead and improves reliability. I would put it differently, hence my aphorism that: "the sign of great architecture is not how well it does the things it was designed to do, but how well it does things you never imagined it would be used for". I suppose you could say that reducing maintenance and improving reliability are examples of the natural consequences of that, but to me those are limited special cases of the more general statement. My sense is that systems decline over time because of what I call 'system cancer': as they are modified to do more and more (new) things, the changes are not usually very cleanly integrated, and eventually one winds up with a big pile. (Examples of this abound; I'm sure we can all think of several.) Noel

4 years, 7 months

Happy birthday, Ada Lovelace and JFO!

by Dave Horsfall

Sorta relevant to both groups... Augusta Ada King-Noel, Countess of Lovelace (and daughter of Lord Byron), was born on this day in 1815; arguably the world's first computer programmer and a highly independent woman, she saw the potential in Charles Babbage's new-fangled invention. J.F.Ossanna was given unto us on this day in 1928; a prolific programmer, he not only had a hand in developing Unix but also gave us the ROFF series. Who'ld've thought that two computer greats would share the same birthday? -- Dave

4 years, 7 months

Re: [TUHS] Were cron and at done at the same time? Or one before the other?

by jnc＠mercury.lcs.mit.edu

> From: Niklas Karlsson > Just consider Multics, or IBM's "Future System". Here's a nice irony for you: one of the key people in killing off FS was reported to me (by someone who should have known) to be Jerry Saltzer (of Multics fame). That wasn't the only time he did something like thst, either; when MIT leaned on him to take over Athena, the first thing he did was to take a lot of their ambitious system plans, and ditch them; they fell back to mostly 'off the shelf' stuff: pretty much vanilla 4.2, etc. Multics itself has an interesting story, quite different from the popular image among those who know little (or nothing) of it. The system, as it was when Honeywell pulled the plug on further generations of new hardware (in the mid-80's) was very different from the system as originally envisaged by MIT (in the mid-60's); it had undergone a massive amount 'experience-based evolution' during those 20 years. For instance, the original concept was to have a process per command (like Unix), but that was dropped early on (because Multics processes were too 'expensive'); they wound up going with doing commands with inter-segment procedure calls. (Which has the nice benefit that when a command faults, you can get dropped right into the debugger, with the failed instance there to look at.) If you read the Organick book on Multics, it describes a much different system: e.g. in Organick there's a 'linkage segment' (used for inter-segment pointers, in pure-code segments) per code segment, but in reality Multics, as distributed, used a single 'combined linkage segment' (which also contained the stack, also unlike the original design, where the stack was a separate segment). There were also numerous places where major sub-systems were re-implemeneted from scratch, with major changes (often great simplifications): one major re-do was the New Storage System, but that one had major new features (based on operationally-shown needs, like the 4.1/.2 Fast File System), so it's not a 'simplification' case. There's one I read about which was much simpler the second time it was implemented, I think it was IPC? Noel

4 years, 7 months

Re: [TUHS] Were cron and at done at the same time? Or one before the other?

by John Foust

At 09:40 AM 12/9/2020, Clem Cole wrote: >My own take on this is what I call "Cole's Law"Â Â Simple economics always beats sophisticated architecture. I thought that was finely sliced cabbage with a tart salad dressing. - John

4 years, 7 months

Were cron and at done at the same time? Or one before the other?

by ron minnich

When I got into Unix in 1976 cron and at were both there. I got to wondering for no particular reason which came first -- I had always assumed cron, but ...? Anyone know?

4 years, 7 months

The origin of Goto considered harmful?

by Bakul Shah

Last night I stumbled upon this speech by Doug McIlroy at Dijkstra's retirement banquet @ UT Austin where he tells the story of his first encounter with EWD and the origins of programming without goto.... Given that we recently had a discussion on "Goto considered harmful", you all may enjoy it. Make sure you watch the start of part 10 as well as that is where the story ends. https://youtu.be/5OUPBwrufKA?list=PL328C7EFFC1F41674&t=326

4 years, 7 months

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TUHS