[Toybox] awk (Re: ps down, top to go)

[Roy Tam]

2016-05-31 11:02 GMT+08:00 Andy Chu <andychup at gmail.com>:
>> If you're restricting it to Bourne compatible, you're cutting out things
>> like Bill Joy's csh and plan 9's "rc"...
>
> Yes, POSIX defines a Bourne-compatible shell.  csh isn't
> Bourne-compatible; I don't think it's ever been standardized.
>
>>> And only 2 of them were started with unpaid labor.  They are:
>>>
>>> - Almquist shell (dash, NetBSD ash, busybox default sh)
>>> - zsh (arguably not posix compatible, but it can be made posix
>>> compatible by setting lots of flags)
>>> - bash
>>
>> The Bourne Again shell was not the original Bourne shell, so I'm already
>> confused by your selection criteria...
>
> I think the original Bourne shell was only available under a paid
> license, so it wasn't FOSS (even though neither of those terms had
> been invented).  Also, the original Bourne shell wasn't POSIX
> compliant.  POSIX added a bunch of things like !.
>
> AFAIK ksh was the dominant implementation at the time of
> standardization, and a lot of its choices made it into the standard,
> with bash closely following POSIX/ksh.
>
>>> - Korn shell and derivatives (pdksh, mksh)  Solaris uses a derivative
>>> of Korn shell.
>>
>> Um, ksh was based on the unix 7 bourne shell? So this is where bourne
>> slots into your taxonomy...?
>
> Yeah that's probably true.  My claim is that there are only 4 code
> open source code lineages for a POSIX compliant shell.
>
> This claim should be easy to disprove: show me some source code which
> implements a POSIX shell, and doesn't share a common ancestor with one
> of the four I mentioned.
>

It will be nice to count OpenSolaris /bin/sh in (CDDL license)
https://hg.openindiana.org/sustaining/oi_151a/illumos-gate/file/711401aaa206/usr/src/cmd/sh

>
>> For IP reasons, Minix and Coherent had their own shells written from
>> scratch. In busybox lash and hush were fresh rewrites (and hush is
>> reasonably usable on nommu, ash doesn't build for that). I believe david
>> bell wrote sash from scratch. There are _several_ different craptacular
>> shells in uclinux (nwsh is 775 lines of C and msh "minimal shell" is
>> _53_ lines of C. Through use of horrible macros. But it has pipe and
>> redirect!)
>
> Actually I poked at hush last night, and actually I think it counts as
> #5.  It's the newest one, started in 2001 by Larry Doolittle.  It has
> some trivial problems like ~ expansion being nonexistent, so it's
> technically not POSIX compliant, but I think the spirit is there.  A
> lot of things work, and it's 10K LOC.  I think it's the closest in
> architecture to my implementation that I've seen.
>
> Most toy shells are more like a Thompson shell -- they implement
> commands and redirections and pipes, but not the Pascal-like
> procedural language that is what Bourne added, and what POSIX
> requires.
>
> My research led me to believe that Minix uses an Almquist Shell
> derivative like NetBSD.  Which Minix shell are you talking about?  If
> it fits my criteria, it should be available to inspect.
>
> If something is 775 lines of C, there is no way it can be POSIX
> compliant, and thus not really worth talking about here.
>
>
>> Plus other oddballs like
>> https://en.wikipedia.org/wiki/Friendly_interactive_shell and
>> https://en.wikipedia.org/wiki/BeanShell and
>> https://en.wikipedia.org/wiki/Scsh and so on. A friend of mine's website
>> used to give you a shell prompt, implemented in javascript...
>
> None of those are remotely close to  POSIX shells...
>
>
>>> It takes 5,000-10,000 LOC to make a POSIX compatible shell,
>>
>> Nah.
>
> OK there's only one way to settle that argument :)  I don't think you
> can do it with 5K LOC even not counting the common toybox code.  And
> certainly not if you count all the lines the shell depends on.
>
> I have an extensive test suite.  I think hush will qualify but I
> haven't tested it yet.  hush might be fairly compliant at the language
> level, but it's not as usable interactively (which is why it's not the
> default in busybox?)
>
> hush is 10 KLOC (+libs), which is the smallest.  busybox ash is 13
> KLOC (+libs).  dash is about 19 KLOC, and mksh 31 KLOC.
>
> I think a POSIX shell will be 5K-10K LOC, but a *usable* POSIX shell
> will be 10K - 15K.  There are a lot of things people expect these
> days.
>
>> The first commercial Unix clone shipped in 1980:
>>
>>   https://en.wikipedia.org/wiki/Coherent_(operating_system)
>>
>> Dennis Ritchie was sent by AT&T to audit it, and confirmed that there
>> was no AT&T code in there.
>
> Sure, but the question is if it had a POSIX shell.  I doubt it.  Like
> I said, most people at that time probably shipped a Thompson-like
> shell, without functions and control flow.
>
>> There were lots of other lineages too, many lost to history in AT&T's
>> great System V push, which also gutted a lot of the BSD use. (That's why
>> IBM's AOS (https://en.wikipedia.org/wiki/IBM_Academic_Operating_System)
>> got rebooted as AIX, and SunOS got rebooted as Solaris: because AT&T was
>> pushing people to use its System V intead of BSD, and using vague legal
>> threats to do it, which Berkeley's Computer Science Research Group
>> eventually successfully fought off in
>> https://www.bell-labs.com/usr/dmr/www/bsdi/bsdisuit.html but that took
>> until 1993 to wrap up, by which point Linux was 2 years old.)
>>
>> This of course predated posix by many years, but it shows that there's a
>> lot of different taxonomies out there.
>
> OK, but again my claim is easy to disprove if it's incorrect.  I'm
> talking about open source POSIX compliant shells.  I claim there are 4
> distinct code lineages (with hush being a probable 5th).  You need a
> significant chunk of code and a lot of testing to make a POSIX
> compliant shell; it won't just happen by accident.  It's not a weekend
> project.  :)
>
> Andy
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