* Re: Thoughts on a builtin read
@ 1993-09-21 15:56 malte
1993-09-21 17:02 ` Chris Siebenmann
0 siblings, 1 reply; 17+ messages in thread
From: malte @ 1993-09-21 15:56 UTC (permalink / raw)
To: rc
[ rsalz@osf.org wrote ]:
Anyhow, let's take a look at your idea. That is,
x=`foobar
hould set $status to the exit value of foobar. What should
x=foobar
set $status to? Leave it unchanged? What about
x=*
if the directory is empty? And if it isn't? What about
x=/foo/*
when /foo doesn't exist?
Yes, an assignment leaves the status unchanged. Your file name expansion
examples are just a shorthand for
x = `{ glob /foo/* } # glob == echo
Currently, neither "x=*" nor "x=`{ glob *}" sets $status to some reasonable
value, it is just 0 -- always!
You are making a simple shell very complicated, don't you think?
Complicated is your word for it, I'd rather call it more usable. I have
frequently had the problem to distinguish between a failed backquote
command and a command producing no output. There may be better solutions then
this
x = `{ foo || echo '!@#$%^&*()' }
if( ~ $x '!@#$%^&*()' )
...
but it seems to me to be a FAQ. The person who started this thread had
just this problem. I don't mean to offend anybody, but I have the impression
that because Tom Duff invented this shell there can't be anything wrong. But
if one takes a closer look, one sees quite a few sh'isms still in it, e.g
shift. I think rc in its original form and in its current form is an excellent
point to start a shell project. This is why I post all this to this list
and have it discussed instead of just implementing it for myself. Be assured
though, that I very much appreciate different opinions.
Back to the read problem: Currently there is no builtin which assigns
a value to a variable ( except for the special variables of course ).
There's been a discussion on shift shifting arbitrary lists with the
proposed syntax being "shift x 2" probably because "x = `{ shift x 2 }"
isn't too elegant. If this makes its way into rc, I don't mind if read
expects a variable as a command line parameter. But since I don't care
if some functionality is built into the shell, I'd prefer the
backquote substitution solution.
Malte
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
1993-09-21 15:56 Thoughts on a builtin read malte
@ 1993-09-21 17:02 ` Chris Siebenmann
0 siblings, 0 replies; 17+ messages in thread
From: Chris Siebenmann @ 1993-09-21 17:02 UTC (permalink / raw)
To: rc
Malte brings up the desire for shift to shift things besides $*.
This has been thoroughly beaten to death in the mailing list; see my
message <91Sep11.132925edt.2708@hawkwind.utcs.toronto.edu>, which has
a supershift function which involves no backquotes and no risk of
carefully quoted variables 'escaping'.
You can find it in the first mailing list archive on archone.tamu.edu,
/pub/rc/rc-list.1991.Z. I highly recommend reading the mailing list
archives; many issues have been discussed and summarized there.
- cks
[to save people's time, here's the function again:
# 'supershift' function for rc.
# usage:
# sshift varname
# sshift varname number
# shifts the list varname by number (default 1) positions.
fn sshift { if (~ $#* 1 ) { _sshift $1 1 $$1 } else { _sshift $1 $2 $$1 } }
# this function does most of the work.
# _sshift NAME COUNT LISTELEMS
# shift LISTELEMS COUNT items left, and assign the result to NAME.
fn _sshift { _vn=() { _vn=$1; shift; shift $1; shift; $_vn=$* } }
]
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
@ 1993-09-22 17:18 Steve_Kilbane
0 siblings, 0 replies; 17+ messages in thread
From: Steve_Kilbane @ 1993-09-22 17:18 UTC (permalink / raw)
To: arnold; +Cc: rc
> I think if people put Plan 9 into production for day to day use,
> including grungy things like writing papers, they might end up with
> more productive environments for themselves. (This would be true of other
> os's as well, eg Clouds here at GT.)
maybe. depends on whether they had access to other machines, too. at
minster.york.ac.uk, the students use a plan 9-like os running on 386 boxes,
but last i saw, i hadn't seen any students doing anything more than running
a load of remote shells onto the file server (which happens to run AIX). me,
i'd play with the local os, and have fun, but generally it doesn't look that
different from unix anyway (the shared environment and lack of links are the
main places where you see the join) - it's only when you get into the
programming that you see where the kludges have been removed.
> Maybe I'm wrong. But the attitude of "I just want to get my job done, I don't
> care about elegance/non-elegance of my environment" just leads us to
> DOS, Novell, and Windows NT. Yuck.
kinda, but inertia was the main thing for dos, and pretty icons is the big
mover for nt, i reckon. it's a sad world.
still, this is off the track of rc. 9fans might be better, but i doubt it.
steve
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
@ 1993-09-21 17:26 Arnold Robbins
0 siblings, 0 replies; 17+ messages in thread
From: Arnold Robbins @ 1993-09-21 17:26 UTC (permalink / raw)
To: rc
> >Alas, the commercial world is just now discovering Unix, and the universities
> >(at least around here) just want to Get The Next Paper Written using frame
> >or whatever. Heaven forbid they should actually *use* an experimental, but
> >state of the art distributed system.
>
> Why would anyone who wants to write a paper want to use a research system?
It is my contention that much of the usability/success of Unix came from the
fact that it was *used*, and not just built and then mined for research
results, the way most university os's are.
I think if people put Plan 9 into production for day to day use,
including grungy things like writing papers, they might end up with
more productive environments for themselves. (This would be true of other
os's as well, eg Clouds here at GT.)
Maybe I'm wrong. But the attitude of "I just want to get my job done, I don't
care about elegance/non-elegance of my environment" just leads us to
DOS, Novell, and Windows NT. Yuck.
Arnold
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
@ 1993-09-21 17:11 rsalz
0 siblings, 0 replies; 17+ messages in thread
From: rsalz @ 1993-09-21 17:11 UTC (permalink / raw)
To: rc-owner, rc
>Alas, the commercial world is just now discovering Unix, and the universities
>(at least around here) just want to Get The Next Paper Written using frame
>or whatever. Heaven forbid they should actually *use* an experimental, but
>state of the art distributed system.
Why would anyone who wants to write a paper want to use a research system?
/r4
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
@ 1993-09-21 16:58 Arnold Robbins
0 siblings, 0 replies; 17+ messages in thread
From: Arnold Robbins @ 1993-09-21 16:58 UTC (permalink / raw)
To: rc
> Is it time to move onto something else?
It has been for some time, now. Why do you think Plan 9 was invented?
Alas, the commercial world is just now discovering Unix, and the universities
(at least around here) just want to Get The Next Paper Written using frame
or whatever. Heaven forbid they should actually *use* an experimental, but
state of the art distributed system.
"Unix is dead, and not only that, it's starting to smell pretty bad too."
-- Rob Pike
I don't believe in The Gospel According to Pike for everything, but a lot
of the time he's right...
Just spouting off steam,
Arnold
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
@ 1993-09-21 16:52 gjv%atlas%cesar
0 siblings, 0 replies; 17+ messages in thread
From: gjv%atlas%cesar @ 1993-09-21 16:52 UTC (permalink / raw)
To: rc%hawkwind.utcs.toronto.edu%m_internet%m_mailnow%hermes.DECnet
[Malte wrote:]
|[ rsalz@osf.org wrote ]:
| set $status to? Leave it unchanged? What about
| x=*
| if the directory is empty? And if it isn't? What about
This sets x to '*', no error whatsoever.
| x=/foo/*
| when /foo doesn't exist?
This sets x to '/foo/*', again no error.
|Yes, an assignment leaves the status unchanged. Your file name expansion
|examples are just a shorthand for
| x = `{ glob /foo/* } # glob == echo
I agree on this, It would be nice if the status reflects the result of
the evaluation of the right-hand side, not that of the assignment itself.
If you 'redefine' $status this way, it is also possible to save and
restore its value, something you currently can't (see my earlier mail
on the problems with $status and the prompt function).
The only problem here may be the following:
; a=(b c)
; $a="foo"
multi-word variable name
; echo $status
1
However, an rc-script aborts if you try this, so you can't check $status
anyway.
|There's been a discussion on shift shifting arbitrary lists with the
|proposed syntax being "shift x 2" probably because "x = `{ shift x 2 }"
|isn't too elegant. If this makes its way into rc, I don't mind if read
|expects a variable as a command line parameter.
As Chris said, a `BUILTIN currently always forks, which is a disadvantage
of an implementation like "x=`{shift x 2}" or "x=`{read a; echo $a}" in order
to get a set of words in 'x'.
And since the $$<var-name> construction already allows a function like
'append x (a b c)' in order to modify the variable 'x', a 'read x'
or 'shift x 2' is not introducing something new.
Personally, I think that
s = shift 2 $s
s = shift 2 (what ever list)
l = read
l2 = read [1=3] # would this read from descriptor 3 ?
would also be quite elegant, avoiding the builtins taking variable
names. But as mentioned above, this causes problems with the current
implementation of $status.
Gert-Jan
---------------------------------------------------
J.G. Vons E-Mail: vons@cesar.crbca1.sinet.slb.com
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
1993-09-21 16:36 Byron Rakitzis
@ 1993-09-21 16:50 ` Chris Siebenmann
0 siblings, 0 replies; 17+ messages in thread
From: Chris Siebenmann @ 1993-09-21 16:50 UTC (permalink / raw)
To: rc
IMHO this is thus an argument against read as a backquote operator,
since one strong reason to put it into the shell in the first place
is for efficiency reasons.
I'm not particularly eager to see someone have to change rc's
perfectly fine and working i/o system for backquote operators.
- cks
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
@ 1993-09-21 16:36 Byron Rakitzis
1993-09-21 16:50 ` Chris Siebenmann
0 siblings, 1 reply; 17+ messages in thread
From: Byron Rakitzis @ 1993-09-21 16:36 UTC (permalink / raw)
To: cks, rc
cks:
> If rc's read becomes a builtin version of line, I think we need some
>optimization of forks in rc, since currently
> x = `BUILTIN
>results in rc forking.
I don't see how this could be avoided unless you define a whole
new i/o model internal to rc just for builtins and the backquote
splitter to use.
It looks like that would involve reinventing the OS inside rc, so it
would lead me to suggest that Unix fork is just broken (i.e., it should
be faster) but this is not a very productive avenue to pursue.
It's a shame when you can't use the Unix style when programming in
Unix. Is it time to move onto something else?
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
@ 1993-09-21 15:54 Tom Culliton x2278
0 siblings, 0 replies; 17+ messages in thread
From: Tom Culliton x2278 @ 1993-09-21 15:54 UTC (permalink / raw)
To: rc
Oh, where to start....
Rich is right about the patch for nalloc.c, his version is better style.
For Malte, simplicity is often the same as usability, it takes a lot
fewer brain cells to remember and correctly use something simple vs.
something complex. Maybe I'm just getting old, but I find myself
running low on brain cells pretty regularly these days. What really
convinced me that rc's read should be simple was looking at the one in
ksh. What a monstrosity! 8-P
The other idea that Malte mentioned, having read act like line, does
have a certain appeal. It's may even be cleaner because it doesn't add
another way of setting variables. And as Alan points out, a simple
function can easily convert one form to the other. The only problem is
that you always need a `{} and thus an extra fork to do anything with
it.
For Chris, if you don't care about setting a different ifs, you can
split the line without a fork by using eval:
read x;eval 'x=('$x')'
Of course if you want to split up the fields of /etc/passwd on ':'
you'll still need to fork. Producing your own version of read, that
splits the input line using ifs, should be easy if you generalize the
backquote code in glom.c. Go for it! ;-)
Finally, Alan has given me the go ahead to repost his version of read as
a patch. The current version doesn't support readline yet, so maybe
I'll try to hack that in after lunch.
Tom
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
@ 1993-09-21 15:15 Alan Watson
0 siblings, 0 replies; 17+ messages in thread
From: Alan Watson @ 1993-09-21 15:15 UTC (permalink / raw)
To: rc
>This is an inconsistency. I'd very much prefer the usual
> "x = `read"
> or "x = `` ( $some_ifs_list ) { read }"
Something along the lines of:
fn read {
if (builtin read LINE) {
echo $LINE
return 0
} else {
echo $LINE
return 1
}
}
I would not mind Malte's suggestion as the primitive -- it seems fairly
easy to convert one to the other with a simple function.
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
@ 1993-09-21 15:09 rsalz
0 siblings, 0 replies; 17+ messages in thread
From: rsalz @ 1993-09-21 15:09 UTC (permalink / raw)
To: rc
>Well, let me put it this way: I always wanted $status to reflect
>the exit status of the backquote command, not the assignment.
Let me make sure I understand. You want to be able to write this:
x=`read
I understand the consistency argument. Since most uses of read will be
in a "read until EOF loop," however, you would require that other changes
be made to rc. I think this is enough to kill your idea.
Anyhow, let's take a look at your idea. That is,
x=`foobar
should set $status to the exit value of foobar. What should
x=foobar
set $status to? Leave it unchanged? What about
x=*
if the directory is empty? And if it isn't? What about
x=/foo/*
when /foo doesn't exist?
You are making a simple shell very complicated, don't you think?
/r$
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
@ 1993-09-21 14:33 malte
0 siblings, 0 replies; 17+ messages in thread
From: malte @ 1993-09-21 14:33 UTC (permalink / raw)
To: rc
[ rsalz@osf.org wrote ]:
> This is an inconsistency. I'd very much prefer the usual
> "x = `read"
> or "x = `` ( $some_ifs_list ) { read }"
Please explain how you would write a "read until EOF loop".
Don't confuse EOF with blank lines.
Well, let me put it this way: I always wanted $status to reflect
the exit status of the backquote command, not the assignment.
To give another example of my "disgustingly bad taste", this will
allow
"while( x = `{ ... } ) ..."
to work, too.
Malte
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
@ 1993-09-21 14:20 rsalz
0 siblings, 0 replies; 17+ messages in thread
From: rsalz @ 1993-09-21 14:20 UTC (permalink / raw)
To: malte, rc
> This is an inconsistency. I'd very much prefer the usual
> "x = `read"
> or "x = `` ( $some_ifs_list ) { read }"
Please explain how you would write a "read until EOF loop".
Don't confuse EOF with blank lines.
I think Tom's list is right-on.
/r$
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
1993-09-21 6:51 malte
@ 1993-09-21 14:19 ` Chris Siebenmann
0 siblings, 0 replies; 17+ messages in thread
From: Chris Siebenmann @ 1993-09-21 14:19 UTC (permalink / raw)
To: rc
If rc's read becomes a builtin version of line, I think we need some
optimization of forks in rc, since currently
x = `BUILTIN
results in rc forking.
- cks
^ permalink raw reply [flat|nested] 17+ messages in thread
* Re: Thoughts on a builtin read
@ 1993-09-21 6:51 malte
1993-09-21 14:19 ` Chris Siebenmann
0 siblings, 1 reply; 17+ messages in thread
From: malte @ 1993-09-21 6:51 UTC (permalink / raw)
To: rc
[ Tom Culliton x2278 wrote: ]
To keep things in the spirit of rc, simplicity should be our guiding
principle. This shapes most of the design decisions discussed below.
I always thought useability was the point ..
1) One string rather than IFS seperation of fields
- simplicity
- preserves information, such as runs of blanks
- field splitting can always be done later with backquote:
read x;x=(`{echo -- $x})
...
4) Should strip the newline
- This makes "read x;echo -- $x" work right.
5) Doesn't honor \ at EOL for continuation
- simplicity
This is an inconsistency. I'd very much prefer the usual
"x = `read"
or "x = `` ( $some_ifs_list ) { read }"
Malte
^ permalink raw reply [flat|nested] 17+ messages in thread
* Thoughts on a builtin read
@ 1993-09-20 22:11 Tom Culliton x2278
0 siblings, 0 replies; 17+ messages in thread
From: Tom Culliton x2278 @ 1993-09-20 22:11 UTC (permalink / raw)
To: rc
After all the recent discussion about builtin read, it is starting to
sound like something that will happen, at the very least as a common
addon. Given this, it's time to examine the design options and try to
come up with something reasonable. After a bit of thought I came up
with the following:
To keep things in the spirit of rc, simplicity should be our guiding
principle. This shapes most of the design decisions discussed below.
1) One string rather than IFS seperation of fields
- simplicity
- preserves information, such as runs of blanks
- field splitting can always be done later with backquote:
read x;x=(`{echo -- $x})
2) Single variable rather than multiple variables
- simplicity
- you can always split the fields as above and use subscripts
3) Good behaviour on EOF.
- return 1 on EOF, 0 otherwise
- save any text on the line before EOF
4) Should strip the newline
- This makes "read x;echo -- $x" work right.
5) Doesn't honor \ at EOL for continuation
- simplicity
6) If interactive and compiled with readline, use that to get input.
- consistency
Aside from the last item, Alan Watson has already presented what looks
like a reasonable implementation way back on May 17th of this year. (It
could be packaged a bit better to fit in with the current addon scheme
and be easier to install.) The case for a builtin read could be much
better evaluated if some folks would try his version and report back on
their experiances.
Tom
PS - with Alan's permission I'll repackage his read routine as a proper
patch so it's easier to try. Alan?
^ permalink raw reply [flat|nested] 17+ messages in thread
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Thread overview: 17+ messages (download: mbox.gz / follow: Atom feed)
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1993-09-21 15:56 Thoughts on a builtin read malte
1993-09-21 17:02 ` Chris Siebenmann
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1993-09-22 17:18 Steve_Kilbane
1993-09-21 17:26 Arnold Robbins
1993-09-21 17:11 rsalz
1993-09-21 16:58 Arnold Robbins
1993-09-21 16:52 gjv%atlas%cesar
1993-09-21 16:36 Byron Rakitzis
1993-09-21 16:50 ` Chris Siebenmann
1993-09-21 15:54 Tom Culliton x2278
1993-09-21 15:15 Alan Watson
1993-09-21 15:09 rsalz
1993-09-21 14:33 malte
1993-09-21 14:20 rsalz
1993-09-21 6:51 malte
1993-09-21 14:19 ` Chris Siebenmann
1993-09-20 22:11 Tom Culliton x2278
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