* problem piping output of shell builtin
@ 2004-01-05 19:26 gj
2004-01-05 20:36 ` Pavol Juhas
2004-01-05 20:44 ` Vincent Stemen
0 siblings, 2 replies; 6+ messages in thread
From: gj @ 2004-01-05 19:26 UTC (permalink / raw)
To: zsh-users
Hi all,
I'm migrating from bash to zsh. It hasn't been so bad because I'm sort of new
to shell programming anyways ( though I did have "fun" figuring out that zsh
arrays start incrementing from 1 as opposed to bash's 0 :). I thought I'd
share the latest hiccup...
Why can't I pipe the output of 'jobs' thusly?
% zsh --version
zsh 4.0.7 (alpha--netbsd)
% sleep 100
^Z
zsh: suspended sleep 100
% sleep 100
^Z
zsh: suspended sleep 100
% jobs
[1] suspended pine
[2] - suspended sleep 100
[3] + suspended sleep 100
% jobs | while read line; do echo $line; done
%
I expect the output of last sequence of commands to be more or less the same
to the sequence before it, as under bash. How can I approximate the bashlike
behavior I expect under zsh?
Thanks for any insight,
Gerald.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: problem piping output of shell builtin
2004-01-05 19:26 problem piping output of shell builtin gj
@ 2004-01-05 20:36 ` Pavol Juhas
2004-01-05 21:30 ` Vincent Stemen
2004-01-05 20:44 ` Vincent Stemen
1 sibling, 1 reply; 6+ messages in thread
From: Pavol Juhas @ 2004-01-05 20:36 UTC (permalink / raw)
To: zsh-users
On Mon, Jan 05, 2004 at 07:26:15PM +0000, gj@sdf.lonestar.org wrote:
> Hi all,
>
> I'm migrating from bash to zsh. It hasn't been so bad because I'm sort of new
> to shell programming anyways ( though I did have "fun" figuring out that zsh
> arrays start incrementing from 1 as opposed to bash's 0 :). I thought I'd
> share the latest hiccup...
>
> Why can't I pipe the output of 'jobs' thusly?
AFAIK, all the shells run one side of the pipe in a subshell. bash
executes subshell for the right side of the pipe, however zsh does
so for the left side. Therefore the `jobs' command in
`jobs|read line' is evaluated in the subshell of zsh, which has no
knowledge about processes in the parent shell - and produces no
output. Left side subshell is however advantageous in other
situations, just compare
zsh -c 'echo 10|read a; echo .$a'
.10
bash -c 'echo 10|read a; echo .$a'
.
To access information in the zsh job table, you need to use the
builtin associate arrays jobtexts, jobstates and jobdirs, for example:
for j in ${(k)jobstates}; do
print -- "[$j] ${jobstates[$j]} ${jobtexts[$j]} in ${jobdirs[$j]}"
done
HTH,
Pavol
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: problem piping output of shell builtin
2004-01-05 19:26 problem piping output of shell builtin gj
2004-01-05 20:36 ` Pavol Juhas
@ 2004-01-05 20:44 ` Vincent Stemen
1 sibling, 0 replies; 6+ messages in thread
From: Vincent Stemen @ 2004-01-05 20:44 UTC (permalink / raw)
To: zsh-users
On Mon, Jan 05, 2004 at 07:26:15PM +0000, gj@sdf.lonestar.org wrote:
> Hi all,
>
> I'm migrating from bash to zsh. It hasn't been so bad because I'm sort of new
> to shell programming anyways ( though I did have "fun" figuring out that zsh
> arrays start incrementing from 1 as opposed to bash's 0 :). I thought I'd
> share the latest hiccup...
>
> Why can't I pipe the output of 'jobs' thusly?
>
> % zsh --version
> zsh 4.0.7 (alpha--netbsd)
> % sleep 100
> ^Z
> zsh: suspended sleep 100
> % sleep 100
> ^Z
> zsh: suspended sleep 100
> % jobs
> [1] suspended pine
> [2] - suspended sleep 100
> [3] + suspended sleep 100
> % jobs | while read line; do echo $line; done
> %
>
> I expect the output of last sequence of commands to be more or less the same
> to the sequence before it, as under bash. How can I approximate the bashlike
> behavior I expect under zsh?
>
> Thanks for any insight,
> Gerald.
That's interesting. I get the same result as you on zsh-4.0.9 but
when I tried it on zsh-4.1.0-dev-5 it works properly.
<test>
$ zsh --version
zsh 4.1.0-dev-5 (i386-portbld-freebsd5.0)
$ sleep 100
^Z
zsh: suspended sleep 100
$ sleep 100
^Z
zsh: suspended sleep 100
$ jobs | while read line; do echo $line; done
[1] - suspended sleep 100
[2] + suspended sleep 100
$
</test>
However, if I pipe the output of some other command like "ls", to the
while loop, it works fine. The problem seems to only be when piping
the output of jobs.
Vincent
--
Vincent Stemen
Avoid the VeriSign/Network Solutions domain registration trap!
http://www.InetAddresses.net
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: problem piping output of shell builtin
2004-01-05 20:36 ` Pavol Juhas
@ 2004-01-05 21:30 ` Vincent Stemen
2004-01-06 1:24 ` Bart Schaefer
2004-01-06 1:39 ` Pavol Juhas
0 siblings, 2 replies; 6+ messages in thread
From: Vincent Stemen @ 2004-01-05 21:30 UTC (permalink / raw)
To: zsh-users
On Mon, Jan 05, 2004 at 03:36:38PM -0500, Pavol Juhas wrote:
> On Mon, Jan 05, 2004 at 07:26:15PM +0000, gj@sdf.lonestar.org wrote:
> > Hi all,
> >
> > I'm migrating from bash to zsh. It hasn't been so bad because I'm sort of new
> > to shell programming anyways ( though I did have "fun" figuring out that zsh
> > arrays start incrementing from 1 as opposed to bash's 0 :). I thought I'd
> > share the latest hiccup...
> >
> > Why can't I pipe the output of 'jobs' thusly?
>
> AFAIK, all the shells run one side of the pipe in a subshell. bash
> executes subshell for the right side of the pipe, however zsh does
> so for the left side. Therefore the `jobs' command in
> `jobs|read line' is evaluated in the subshell of zsh, which has no
> knowledge about processes in the parent shell - and produces no
> output. Left side subshell is however advantageous in other
> situations, just compare
>
> zsh -c 'echo 10|read a; echo .$a'
> .10
> bash -c 'echo 10|read a; echo .$a'
> .
>
> To access information in the zsh job table, you need to use the
> builtin associate arrays jobtexts, jobstates and jobdirs, for example:
>
> for j in ${(k)jobstates}; do
> print -- "[$j] ${jobstates[$j]} ${jobtexts[$j]} in ${jobdirs[$j]}"
> done
>
> HTH,
>
> Pavol
Under bash, at least, the semi-colon is ending the pipe command and
then executing "echo .$a" as new command in the original shell. So
you need to group the entire right side in the above example.
ie.
$ echo 10 | (read a; echo .$a)
.10
$
That is interesting. I did not know zsh did that by default.
However, I am not sure you are correct about zsh forking a sub-shell
for the left side of the pipe. If so, then local shell variables from
the parent shell should not be accessible unless they are exported,
but they are.
$ x=foo
$ echo $x | read a; echo .$a
.foo
$
Vincent
--
Vincent Stemen
Avoid the VeriSign/Network Solutions domain registration trap!
http://www.InetAddresses.net
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: problem piping output of shell builtin
2004-01-05 21:30 ` Vincent Stemen
@ 2004-01-06 1:24 ` Bart Schaefer
2004-01-06 1:39 ` Pavol Juhas
1 sibling, 0 replies; 6+ messages in thread
From: Bart Schaefer @ 2004-01-06 1:24 UTC (permalink / raw)
To: zsh-users
This is becoming a very FAQ, right up there with "why can't I see the last
line of my output when it doesn't end in a newline?" I'm not sure why it
has never gotten an actual FAQ entry of its own.
Here's a short answer:
http://www.zsh.org/mla/workers/2003/msg00827.html
Try a search of the mailing list archives:
http://www.zsh.org/cgi-bin/mla/wilma_glimpse/workers?query=pipe%3Bjobs&Search=Search&restricttofiles=on&filelist=2003&filelist=2002&errors=0&maxfiles=50&maxlines=10&.cgifields=filelist&.cgifields=restricttofiles&.cgifields=lineonly&.cgifields=partial&.cgifields=case
http://www.zsh.org/cgi-bin/mla/wilma_glimpse/users?query=pipe%3Bjobs&Search=Search&restricttofiles=on&filelist=2003&filelist=2002&errors=0&maxfiles=50&maxlines=10&.cgifields=filelist&.cgifields=restricttofiles&.cgifields=lineonly&.cgifields=partial&.cgifields=case
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: problem piping output of shell builtin
2004-01-05 21:30 ` Vincent Stemen
2004-01-06 1:24 ` Bart Schaefer
@ 2004-01-06 1:39 ` Pavol Juhas
1 sibling, 0 replies; 6+ messages in thread
From: Pavol Juhas @ 2004-01-06 1:39 UTC (permalink / raw)
To: zsh users
On Mon, Jan 05, 2004 at 03:30:10PM -0600, Vincent Stemen wrote:
> On Mon, Jan 05, 2004 at 03:36:38PM -0500, Pavol Juhas wrote:
> > On Mon, Jan 05, 2004 at 07:26:15PM +0000, gj@sdf.lonestar.org wrote:
...
> > > Why can't I pipe the output of 'jobs' thusly?
> >
> > AFAIK, all the shells run one side of the pipe in a subshell. bash
> > executes subshell for the right side of the pipe, however zsh does
> > so for the left side. Therefore the `jobs' command in
> > `jobs|read line' is evaluated in the subshell of zsh, which has no
> > knowledge about processes in the parent shell - and produces no
> > output. Left side subshell is however advantageous in other
> > situations, just compare
> >
> > zsh -c 'echo 10|read a; echo .$a'
> > .10
> > bash -c 'echo 10|read a; echo .$a'
> > .
...
>
> Under bash, at least, the semi-colon is ending the pipe command and
> then executing "echo .$a" as new command in the original shell. So
> you need to group the entire right side in the above example.
> ie.
>
> $ echo 10 | (read a; echo .$a)
> .10
> $
Exactly, bash has no way to read the output of the pipe to a
variable (well, without creating temporary file).
>
> That is interesting. I did not know zsh did that by default.
> However, I am not sure you are correct about zsh forking a sub-shell
> for the left side of the pipe. If so, then local shell variables from
> the parent shell should not be accessible unless they are exported,
> but they are.
>
> $ x=foo
> $ echo $x | read a; echo .$a
> .foo
> $
Variables are exported to the subshell, but if you change them in
the left-side of the pipe, they will keep the original value in the
parent shell, e.g.
$ a=foo; { a=bar } | :
$ echo $a
foo
$ a=foo; { a=bar }
$ echo $a
bar
$ a=foo; : | { a=bar }
$ echo $a
bar
$ i=foo; for i in 1 2; do echo $i; done | cat; echo $i
1
2
foo
I think the most recent versions of zsh were expanded so they
actually can handle `jobs|read line'.
Pavol
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2004-01-06 1:40 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2004-01-05 19:26 problem piping output of shell builtin gj
2004-01-05 20:36 ` Pavol Juhas
2004-01-05 21:30 ` Vincent Stemen
2004-01-06 1:24 ` Bart Schaefer
2004-01-06 1:39 ` Pavol Juhas
2004-01-05 20:44 ` Vincent Stemen
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