TUHS

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6412 discussions

Re: [TUHS] head/sed/tail (was The Unix shell: a 50-year view)

by Paul Ruizendaal

> Message: 7 > Date: Thu, 15 Jul 2021 10:28:04 -0400 > From: "Theodore Y. Ts'o" > Subject: Re: [TUHS] head/sed/tail (was The Unix shell: a 50-year view) > > On Wed, Jul 14, 2021 at 10:38:06PM -0400, Douglas McIlroy wrote: >> Head might not have been written if tail didn't exist. But, unlike head, >> tail strayed from the tao of "do one thing well". Tail -r and tail -f are >> as cringeworthy as cat -v. >> >> -f is a strange feature that effectively turns a regular file into a pipe >> with memory by polling for new data, A clean general alternative >> might be to provide an open(2) mode that makes reads at the current >> file end block if some process has the file open for writing. > > OTOH, this would mean adding more functionality (read: complexity) > into the kernel, and there has always been a general desire to avoid > pushing <stuff> into the kernel when it can be done in userspace. Do > you really think using a blocking read(2) is somehow more superior > than using select(2) to wait for new data to be appended to the file? > > And even if we did this using a new open(2) mode, are you saying we > should have a separate executable in /bin which would then be > identical to cat, except that it uses a different open(2) mode? Yes, it would put more complexity into the kernel, but maybe it is conceptually elegant. Consider a classic pipe or a socket and the behaviour of read(2) for those objects. The behaviour of read(2) that Doug proposes for a file would make it in line with that for a classic pipe or a socket. Hence, maybe it should not be a mode, but the standard behaviour. I often think that around 1981 the Unix community missed an opportunity to really think through how networking should integrate with the foundations of Unix. It seems to me that at that time there was an opportunity to merge files, pipes and sockets into a coherent, simple framework. If the 8th edition file-system-switch had been introduced already in V6 or V7, maybe this would have happened. On the other hand, the installed base was probably already too large in 1981 to still make breaking changes to core concepts. V7 may have been the last chance saloon for that. Paul

3 years, 5 months

Re: [TUHS] Unix Shell Programming: The Next 50 Years - author's response and my response

by Jon Steinhart

Below is a response from two of the authors with my response to it inline. Not very impressed. Hopefully they'll get a clue and up their game. In any case, enough time spent on it. Jon Michael Greenberg writes: > > HotOS isn't exactly a conventional venue---you might notice that many > if not most HotOS papers don't fit the outline you've given. I'm aware of that, and have participated in many unconventional venues myself. I wasn't saying that papers must fit that outline, but I do believe that they should contain that information. There's a big difference between a discussion transcript and a paper; I believe that papers, especially those published under the auspices of a prestigious organization such as the ACM, should adhere to a higher standard. > I'd definitely appreciate detailed feedback on any semantic errors > we've made! Unfortunately I can't help you here; that was feedback from a reader who doesn't want to spend any more time on this. > Your summary covers much of what we imagined! > > As I understand it, the primary goals of the paper were to (a) help > other academics think about the shell as a viable area for research, (b) > highlight some work we're doing on JIT compilation, (c) make the case > for JIT approaches to the shell in general (as its well adapted to its > dynamism), and (d) explore various axes on which the shell could be > improved. It seems like we've done a good job communicating (b) to you, > but perhaps not the rest. Sorry again to disappoint. I certainly hope that you understand the primary goals of your own paper. Point-by-point: (a) While this is a valid point I don't understand why the paper didn't just state it in a straightforward manner. There are several common forms. One is to list issues in the introduction while explaining which one(s) will be addressed in the paper. Another is in the conclusion where authors list work still to be done. (b) At least for me this goal was not accomplished because there were no examples. Figure 1 by itself is insufficient given that the code used to generate the "result" is not shown. It would have been much more illuminating had the paper not only shown that code but also the optimized result. Professionals don't blithely accept magic data. (c) The paper failed to make this case to me for several reasons. As I understand it, the paper is somewhat about applying JIT compilation techniques to interconnected processes. While most shells include syntax to support the construction of such, it's really independent of the shell. For completeness, I have a vague memory of shell implementations for non-multitasking systems that sequentially ran pipelined programs passing intermediate results via temporary files. The single "result" reminds me of something that I saw at a science fair when my child was in middle school; I looked a one team's results and asked "What makes you think that a sample size of one is significant?" The lack of any benchmarks or other study results that justified the work also undermined the case. It reads more like the authors had something that they wanted to play with rather than doing serious research. The paper does not examine the percentage of shell scripts that actually benefit from JIT compilation; for all the reader may know it's such a small number that hand-optimizing just those scripts might be a better solution. I suppose that the paper fits into the apparently modern philosophy of expecting tools to fix up poorly written code so that programmers don't have to understand what they're doing. (d) In my opinion the paper didn't do this at all. There was no analysis of "the shell" showing weaknesses and an explanation of why one particular path was taken. And there was no discussion of what was being done with shells to cause whatever problems you were addressing and possibly ameliorating problems with some up-front sanity. Again, being a geezer I'm reminded of past events that repeat themselves. I joined a start-up company decades ago that was going to speed up circuit simulation 100x by plugging custom-designed floating-point processing boards into a multiprocessor machine. I managed to beat that 100x just by cleverly crafting the database and memory management code. The fact that the company founder never verified his idea led to a big waste of resources. But, he did manage to raise venture capital which is akin to getting DARPA funds. Nikos Vasilakis writes: > > To add to Michael's points, HotOS' "position" papers are often > intended as provocative, call-to-arms statements targeting primarily > the research community (academic and industrial research). Our key > position, which we possibly failed to communicate, is "Hey researchers > everywhere, let's do more research on the shell! (and here's why)". While provocative name-calling and false statements seem to have become the political norm in America I don't think that they're appropriate in a professional context. In my experience a call-to-arms isn't productive unless those called understand the nature of the call. I'm reminded of something that happened many decades ago; my partner asked me to proof a paper that she was writing for her masters degree. I read it over with a confused look and asked her what she was trying to say. She responded, and I told her to write that down and stop trying to sound like someone else. Turned her into a much better writer. So if the paper wanted to say "Hey researchers ..." it should have done so instead of being obtuse. To continue on this point and Michael's (a) above, I don't see a lot of value in proclaiming that research can be done. I think that a more fruitful approach is to cover what has been done, what you're doing, and what you see but aren't doing. > For our more conventional research papers related to the shell, which > might cover your concerns about semantics, correctness, and > performance please see next. These three papers also provide important > context around the HotOS paper you read: > ... Tracking down your other work was key to understanding this paper. It's my opinion that my having to do is illustrative of the problems with the paper. > Thank you for taking the time to read our paper and comment on it. > Could you please share the emails of everyone mentioned at the end of > your email? We are preparing a longer report on a recent shell > roundtable, and would love to get everyone's feedback! While I appreciate the offer to send the longer report, it would only be of interest if it was substantially more professional. There is no interest in reviewing work that is not clearly presented, has not been proofread and edited, includes unsubstantiated, pejorative, or meaningless statements, includes incorrect examples, or statistically irrelevant results. Likewise, there is also no interest if the homework hasn't been done to put the report in context with regards to prior art and other current work. Jon Steinghart <jsacm(a)fourwinds.com> Warner Losh <imp(a)bsdimp.com> John Cowan <cowan(a)ccil.org> Larry McVoy <lm(a)mcvoy.com> John Dow <jmd(a)nelefa.org> Andy Kosela <akosela(a)andykosela.com> Clem Cole <clemc(a)ccc.com> Steve Bourne does not want to give out his address

3 years, 5 months

Re: [TUHS] head/sed/tail (was The Unix shell: a 50-year view)

by Nelson H. F. Beebe

On the subject of tac (concatenate and print files in reverse), I can report that the tool was written by my late friend Jay Lepreau in the Department of Computer Science (now, School of Computing) at the University of Utah. The GNU coreutils distribution for src/tac.c contains a copyright for 1988-2020. I searched my TOPS-20 PDP-10 archives, and found no source code for tac, but I did find an older TOPS-20 executable in Jay's personal directory with a file date of 17-Mar-1987. There isn't much else in that directory, so I suspect that he just copied over a needed tool from his Department of Computer Science TOPS-20 system to ours in the College of Science. ---------------------------------------- P.S. Jay was the first to get Steve Johnson's Portable C Compiler, pcc, to run on the 36-bit PDP-10, and once we had pcc, we began the move from writing utilities in Pascal and PDP-10 assembly language to doing them in C. The oldest C file for pcc in our PDP-10 archives is dated 17-Mar-1981, with other pcc files dated to mid-1983, and final compiler executables dated 12-May-1986. Four system header files are dated as late as 4-Oct-1986, presumably patched after the compiler was built. Later, Kok Chen and Ken Harrenstien's kcc provided another C compiler that added support for byte datatypes, where a byte could be anything from 1 to 36 bits. The oldest distribution of kcc in our archives is labeled "Fifth formal distribution snapshot" and dated 20-Apr-1988. My info-kcc mailing list archives date from the list beginning, with an initial post from Ken dated 27-Jul-1986 announcing the availability of kcc at sri-nic.arpa. By mid-1987, we had a dozen Sun workstations and NFS fileserver; they marked the beginning of our move to a Unix workstation environment, away from large, expensive, and electricity-gulping PDP-10 and VAX mainframes. By the summer of 1991, those mainframes were retired. I recall speaking to a used-equipment vendor about our VAX 8600, which cost about US$450K (discounted academic pricing) in 1986, and was told that its value was depreciating about 20% per month. Although many of us missed TOPS-20 features, I don't think anyone was sad to say goodbye to VMS. We always felt that the VMS developers worked in isolation from the PDP-10 folks, and thus learned nothing from them. ------------------------------------------------------------------------------- - Nelson H. F. Beebe Tel: +1 801 581 5254 - - University of Utah FAX: +1 801 581 4148 - - Department of Mathematics, 110 LCB Internet e-mail: beebe(a)math.utah.edu - - 155 S 1400 E RM 233 beebe(a)acm.org beebe(a)computer.org - - Salt Lake City, UT 84112-0090, USA URL: http://www.math.utah.edu/~beebe/ - -------------------------------------------------------------------------------

3 years, 5 months

Re: [TUHS] head/sed/tail (was The Unix shell: a 50-year view)

by norman＠oclsc.org

Some comments from someone (me) who tends to be pickier than most about cramming programs together and endless sets of options: I, too, had always thought sed was older than head. I stand corrected. I have a long-standing habit of typing sed 10q but don't spend much time fussing about head. When I arrived at Bell Labs in late summer 1984, tail -f was in /usr/bin and in the manual, readslow was only in /usr/bin. readslow was like tail -f, except it either printed the entire file first or (option -e) started at the end of the file. I was told readslow had come first, and had been invented in a hurry because people wanted to watch in real time the moves logged by one of Belle's chess matches. Vague memory says it was written by pjw; the name and the code style seem consistent with that. Personally I feel like tail -r and tail -f both fit reasonably well within what tail does, since both have to do with the bottom of the file, though -r's implementation does make for a special extra code path in tail so maybe a separate program is better. What I think is a bigger deal is that I have frequently missed tail -r on Linux systems, and somehow hadn't spotted tac; thanks to whoever here (was it Ted?) pointed it out first! On the other hand, adding data-processing functions to cat has never made sense to me. It seems to originate from a mistaken notion that cat's focus is printing data on terminals, rather than concatenating data from different places. Here is a test: if cat -v and cat -n and all that make sense, why shouldn't cat also subsume tr and pr and even grep? What makes converting control characters and numbering lines so different from swapping case and adding page headers? I don't see the distinction, and so I think vis(1) (in later Research) makes more sense than cat -v and nl(1) (in Linux for a long time) more sense than cat -n. (I'd also happily argue that given nl, pr shouldn't number lines. That a program was in V6 or V7 doesn't make it perfect.) And all those special options to wc that amounted to doing arithmetic on the output were always just silly. I'm glad they were retracted. On the other other hand, why didn't I know about tac? Because there are so damn many programs in /usr/bin these days. When I started with UNIX ca. 1980, the manual (even the BSD version) was still short enough that one could sit down and read it through, section by section, and keep track of what one had read, and remember what all the different tools did. That hasn't been true for decades. This could be an argument for adding to existing programs (which many people already know about) rather than adding new programs (which many people will never notice). The real problem is that the system is just too damn big. On an Ubuntu 18.04 system I run, ls /usr/bin | wc -l shows 3242 entries. How much of that is redundant? How much is rarely or never used? Nobody knows, and I suspect few even try to find out. And because nobody knows, few are brave enough to throw things away, or even trim out bits of existing things. One day in the late 1980s, I helped out with an Introduction to UNIX talk at a DECUS symposium. One of the attendees noticed the `total' line in the output of ls, and asked why is that there? doesn't that contradict the principles of tools' output you've just been talking about? I thought about it, and said yes, you're right, that's a bit of old history and shouldn't be there any more. When I got home to New Jersey, I took the `total' line out of Research ls. Good luck doing anything like that today. Norman Wilson Toronto ON

3 years, 5 months

First machine to run rogue?

by Dan Cross

What was the first machine to run rogue? I understand that it was written by Glenn Wichman and Michael Toy at UC Santa Cruz ca. 1980, using the `curses` library (Ken Arnold's original, not Mary Ann's rewrite). I've seen at least one place that indicates it first ran on 6th Edition, but that doesn't sound right to me. The first reference I can find in BSD is in 2.79 ("rogue.doc"), which also appears to be the first release to ship curses. Anyone have any info? Thanks! - Dan C.

3 years, 6 months

[tuhs] The Unix shell: a 50-year view

by Nelson H. F. Beebe

In this week's BSDNow.tv podcast, available at https://www.bsdnow.tv/409 there is a story about a new conference paper on the Unix shell. The paper is available at Unix shell programming: the next 50 years HotOS '21: Workshop on Hot Topics in Operating Systems, Ann Arbor, Michigan, 1 June, 2021--3 June, 2021 https://doi.org/10.1145/3458336.3465294 The tone is overall negative, though they do say nice things about Doug McIlroy and Steve Johnson, and they offer ideas about improvements. List readers will have their own views of the paper. My own is that, despite its dark corners, the Bourne shell has served us extraordinarily well, and I have been writing in it daily for decades without being particularly bothered by the many issues raised by the paper's authors. Having dealt with so-called command shells on numerous other operating systems, at least the Unix shells rarely get in my way. ------------------------------------------------------------------------------- - Nelson H. F. Beebe Tel: +1 801 581 5254 - - University of Utah FAX: +1 801 581 4148 - - Department of Mathematics, 110 LCB Internet e-mail: beebe(a)math.utah.edu - - 155 S 1400 E RM 233 beebe(a)acm.org beebe(a)computer.org - - Salt Lake City, UT 84112-0090, USA URL: http://www.math.utah.edu/~beebe/ - -------------------------------------------------------------------------------

3 years, 6 months

Re: [TUHS] The Unix shell: a 50-year view - hopefully final review of letter

by jnc＠mercury.lcs.mit.edu

> From: Jon Steinhart > I use UNIX instead of Unix as that's what I believe is the correct form. Well, Bell documentation uses "UNIX" through V6: https://minnie.tuhs.org//cgi-bin/utree.pl?file=V6/usr/doc/start/start "Unix" starts to appear with V7: https://minnie.tuhs.org//cgi-bin/utree.pl?file=V7/usr/doc/setup As mentioned, the trademark is "UNIX". I don't really have a fixed position on _the_ way to spell it: when I'm wiriting about a specific version (e.g. V6) I use the capitalization as of that version; for general text I'd probably use 'Unix', as that seems to be general now. But I could easily be convinced otherwise. Noel

3 years, 6 months

The Unix shell: a 50-year view - hopefully final review of letter

by Jon Steinhart

Once again, thanks to everybody who as contributed to making this a better letter. Many of you have asked to be co-signers. Please let me know if I've included your name by mistake or if you'd like your name to be added. And, of course, let me know if any more edits are required. BTW, except where I'm quoting the paper I use UNIX instead of Unix as that's what I believe is the correct form. Please let me know if that's not correct. Thanks, Jon I read the "Unix Shell Programming: The Next 50 Years" paper expecting some well thought out wisdom. I was sorely disappointed. The paper is lacking the generally accepted form of: o What problem are you trying to solve? o What have others done? o What's our approach? o How does it do? Some particulars: o The paper never defines what is meant by the term "Unix shell." I think that you're using it to mean a command interpreter as described in the POSIX 1003.2 documents. o The paper makes liberal use of the term "Unix" such as "... in every Unix distribution." While systems descended from UNIX abound few actual instances of UNIX exist today. o There is no 50-year-old UNIX shell. I started using UNIX in the early 1970s, and the command interpreter at the time (Ken Thompson's shell) was nothing like later shells such as the Bourne shell (sh since research V7 UNIX), Korn shell (ksh), C shell (csh), and the Bourne again shell (bash). UNIX mainstreamed the notion of a command interpreter that was not baked into the system. The paper lacks any discussion of prior art. In practice, shell implementations either predate the POSIX standard or were built afterwards and include non-standard extensions. o The paper repeatedly claims that the shell has been largely ignored by academia and industry. Yet, it does not include any references to support that claim. In fact, the large body of published work on shells and ongoing work on shells such as zsh shows that claim to be incorrect. o The large number of pejorative statements detract from the academic value of the paper. And, in my opinion, these statements are provably false. It reads as if the authors are projecting their personal opinions onto the rest of the world. o The paper applies universal complaints such as "unmaintainable" to the shell; it doesn't call out any shell-specific problems. It doesn't explain whether these complaints are against scripts, implementations, or both. One of the reasons for the longevity of the family of shells descended from Bourne's sh is that experienced practitioners have been able to write easily maintainable code. Scripts written in the 1980s are still around and working fine. o The paper seems to complain about the fact that the shell is documented. This is astonishing. Proper documentation has always been a key component of being a professional, at least in my decades of experience. As a matter of fact, my boss telling me that "nobody will give a crap about your work unless you write a good paper" when I was a teenager at Bell Labs is what led me to UNIX and roff. o The paper includes non-sequiturs such as discussions about Docker and systemd that have nothing to to with the shell. o The paper has many "no-op" statements such as "arguably improved" that provide no useful information. o The example on page 105 don't work as there is no input to "cut". o The single result in Figure 1 is insufficient evidence that the approach works on a wide variety of problems. o The paper gives the appearance that the authors don't actually understand the Bourne shell semantics. Not just my opinion; Steve Bourne expressed that in an email to me after he read your paper, and I consider him to be a subject matter expert. o The paper confuses the performance of the shell with the performance of external commands executed by the shell. o Proofreading should have caught things like "improve performance performance" on page 107 among others. I think that the paper is really trying to say: o Programmable command interpreters such as those found in UNIX based systems have been around for a long time. For this paper, we're focusing on the GNU bash implementation of the POSIX P1003.2 shell. Other command interpreters predate UNIX. o This implementation is used more often than many other scripting languages because it is available and often installed as the default command interpreter on most modern systems (UNIX-based and otherwise). In particular, it is often the default for Linux systems. o The shell as defined above is being used in more complex environments than existed at the time of its creation. This exposes a new set of performance issues. o While much work has been done by the bash implementers, it's primarily been in the area of expanding the functionality, usually in a backward-compatible manner. Other shells such as the original ksh and later ash and zsh were implemented with an eye towards the performance of the internals and user perspectives. o Performance optimization using modern techniques such as JIT compilation have been applied to other languages but not to POSIX shell implementations. This paper looks at doing that. It is unsurprising that techniques that have worked elsewhere work here too. It's hard to imagine that the application of this technique is all that's required for a 50-year life extension. The title of this paper implies that it's going to be comprehensive but instead concentrates on a couple of projects. It ignores other active work on shells such as "fish". While it wouldn't eliminate the issues with the paper, they would not have been quite so glaring had it had a more modest title such as "Improving POSIX Shell Performance with JIT Compilation". Jon Steinhart plus John Cowan, Warner Losh, John Dow, Steve Bourne, Larry McVoy, and Clem Cole

3 years, 6 months

The Unix shell: a 50-year view -- feedback wanted

by Jon Steinhart

I not only found this paper offensive, but was more offended that ACM would publish something like this and give it an award to boot. I'm planning to send the authors and ACM what's below. Would appreciate any feedback that you could provide to make it better. Thanks, Jon I read your "Unix Shell Programming: The Next 50 Years" expecting some well thought out wisdom from learned experiences. I was sorely disappointed. o The paper never defines what is meant by the term "Unix shell." I think that you're using to mean a command interpreter as described in the POSIX 1003.2 documents. o There is no 50 year old Unix shell. I started using Unix in the early 1970s, and the command interpreter at the time (Ken Thompson's shell) was nothing like later shells such as the Bourne shell (sh since research V7 Unix), Korn shell (ksh), C shell (csh), and the Bourne again shell (bash). The paper is missing any discussion of prior art. In practice, shell implementations either predate the POSIX standard or were built afterwards and include non-standard extensions. o The paper repeats a claim that the shell has been largely ignored by academia and industry. Yet, it does not include any references that support that claim. My own experience and thus opinion is the opposite making the veracity of your claim questionable. As a reader, such unsubstantiated claims make me treat the entire content as suspect. o The paper applies universal complaints such as "unmaintainable" to the shell; it doesn't call out any shell-specific problems. It doesn't explain whether these complaints are against the scripts, the implementation, or both. One of the reasons for the longevity of the sh/bash shells is that experienced practicioners have been able to write easily maintainable code. Scripts written in the 1980s are still around and working fine. o The paper seems to complain that the fact that the shell is documented is a problem. This is an astonishing statement. In my decades as an acting professional, teacher, and author, proper documentation is a key component of being a professional. o The paper is full of non-sequiturs such as discussions about Docker and systemd that have nothing to to with the shell. o The paper has many "nop" statements such as "arguably improved" that don't actually say anything. o Examples, such as the one on page 105 don't work. o Proofreading should have caught things like "improve performance performance" on page 107 among others. o The references contain many more items than the paper actually references. Did you plagerize the bibliography and forget to edit it? o The single result in Figure 1 is insufficient evidence that the approach works on a wide variety of problems. o The paper makes it appear that the authors don't actually understand the semantics of the original Bourne shell. Not just my opinion; I received an email from Steve Bourne after he read your paper, and I consider him to be a subject matter expert. The paper is lacking the generally accepted form of: o What problem are you trying to solve? o What have others done? o What's our approach? o How does it do? Filtering out all of the jargon added for buzzword compliance, I think that the paper is really trying to say: o Programmable command interpreters such as those found in Unix-based systems have been around for a long time. For this paper, we're focusing on the GNU bash implementation of the POSIX P1003.2 shell. Other command interpreters predate Unix. o This implementation is used more often than many other scripting languages because it is available and often installed as the default command interpreter on most modern systems (Unix-based or otherwise). In particular, it is often the default for Linux systems. o The shell as defined above is being used in ways that are far more complex than originally contemplated when Bourne created the original syntax and semantics, much less the new features added by the POSIX standards committee. The combination of both the POSIX and bash extensions to the Bourne shell exposes a new set of limitations and issues such as performance. o While much work has been done by the bash implementors, it's primarily been in the area of expanding the functionality, usually in a backward-compatible manner. Other shells such as the original ksh and later ash and zsh were implemented with an eye towards the performance of the internals and user perspectives. o Performance optimization using modern techniques such as JIT have been applied to other languages but not to POSIX shell implementations. This paper looks at doing that. It is unsurprising that techniques that have worked elsewhere work here too. o It's hard to imagine that the application of this technique is all that's required for a 50-year life extension. The title of this paper implies that it's going to be comprehensive rather than just being a shameless plus for an author's project. Of course, this doesn't make much of a paper. Guessing that that's why it was so "bulked up" with irrelevancies. It appears that all of you are in academia. I can't imagine that a paper like this would pass muster in front of any thesis committee, much less get that far. Not only for content, but for lack of proofreading and editing. The fact that the ACM would publish such a paper eliminates any regret that I may have had in dropping my ACM membership.

3 years, 6 months

The Unix shell: a 50-year view -- second pass feedback wanted

by Jon Steinhart

Thanks to everyone who provided me feedback on the first pass, especially those who suggested "shopt -u flame-off". Here's the second version. Once again, would appreciate feedback. Thanks, Jon I read your "Unix Shell Programming: The Next 50 Years" expecting some well thought out wisdom. I was sorely disappointed. The paper is lacking the generally accepted form of: o What problem are you trying to solve? o What have others done? o What's our approach? o How does it do? Some particulars: o The paper never defines what is meant by the term "Unix shell." I think that you're using it to mean a command interpreter as described in the POSIX 1003.2 documents. o There is no 50 year old Unix shell. I started using Unix in the early 1970s, and the command interpreter at the time (Ken Thompson's shell) was nothing like later shells such as the Bourne shell (sh since research V7 Unix), Korn shell (ksh), C shell (csh), and the Bourne again shell (bash). Unix mainstreamed the notion of a command interpreter that was not baked into the system. The paper lacks any discussion of prior art. In practice, shell implementations either predate the POSIX standard or were built afterwards and include non-standard extensions. o The paper repeats a claim that the shell has been largely ignored by academia and industry. Yet, it does not include any references that support that claim. In fact, the large body of published work on shells and ongoing work on shells such as zsh shows that claim to be incorrect. o The paper applies universal complaints such as "unmaintainable" to the shell; it doesn't call out any shell-specific problems. It doesn't explain whether these complaints are against the scripts, the implementation, or both. One of the reasons for the longevity of the family of shells descended from Bourne's sh is that experienced practicioners have been able to write easily maintainable code. Scripts written in the 1980s are still around and working fine. o The paper seems to complain that the fact that the shell is documented is a problem. This is astonishing. Proper documentation has always been a key component of being a professional in my decades of experience. As a matter of fact, my boss telling me that "nobody will give a crap about your work unless you write a good paper" when I was a teenager at Bell Labs is what led me to UNIX and nroff. o The paper includes non-sequiturs such as discussions about Docker and systemd that have nothing to to with the shell. o The paper has many "nop" statements such as "arguably improved" that don't actually say anything. o Examples, such as the one on page 105 don't work as there is no input to "cut". o The single result in Figure 1 is insufficient evidence that the approach works on a wide variety of problems. o The paper gives the appearance that the authors don't actually understand the semantics of the original Bourne shell. Not just my opinion; I received an email from Steve Bourne after he read your paper, and I consider him to be a subject matter expert. o Proofreading should have caught things like "improve performance performance" on page 107 among others. I think that the paper is really trying to say: o Programmable command interpreters such as those found in Unix-based systems have been around for a long time. For this paper, we're focusing on the GNU bash implementation of the POSIX P1003.2 shell. Other command interpreters predate Unix. o This implementation is used more often than many other scripting languages because it is available and often installed as the default command interpreter on most modern systems (Unix-based or otherwise). In particular, it is often the default for Linux systems. o The shell as defined above is being used in ways that are far more complex than originally contemplated when Bourne created the original syntax and semantics, much less the new features from kash adopted by the POSIX standards committee. The combination of both the POSIX and bash extensions to the Bourne shell exposes a new set of limitations and issues such as performance. o While much work has been done by the bash implementors, it's primarily been in the area of expanding the functionality, usually in a backward-compatible manner. Other shells such as the original ksh and later ash and zsh were implemented with an eye towards the performance of the internals and user perspectives. o Performance optimization using modern techniques such as JIT compilation have been applied to other languages but not to POSIX shell implementations. This paper looks at doing that. It is unsurprising that techniques that have worked elsewhere work here too. It's hard to imagine that the application of this technique is all that's required for a 50-year life extension. The title of this paper implies that it's going to be comprehensive but instead concentrates on a couple of projects. It ignores other active work on shells such as "fish". While the issues with the paper remain, they would not have been quite so glaring had it had a more modest title such as "Applying JIT Compilation to the POSIX Shell".

3 years, 6 months

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