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* kill the LHS command of a pipe once the RHS command terminates
@ 2019-06-28 11:04 Vincent Lefevre
  2019-06-28 11:38 ` Vincent Lefevre
                   ` (2 more replies)
  0 siblings, 3 replies; 20+ messages in thread
From: Vincent Lefevre @ 2019-06-28 11:04 UTC (permalink / raw)
  To: zsh-users

With some commands I pipe the output to a pager, and when quitting
the pager, I want the command to terminate immediately (so that it
doesn't consume more resources) and want the shell prompt back.

Here are examples with "head -n 1" instead of a pager.

* With just a pipe:

zira% { echo foo; sleep 3; echo err >&2 } | head -n 1
foo
[wait for 3 seconds]
err
zira%

The issue is that when "head -n 1" terminates (just after "echo foo"),
the left-hand-side command is still running. Thus it still consumes
resources, and I also have to wait for the shell prompt, which is bad.

* With a process substitution:

zira% head -n 1 <(echo foo; sleep 3; echo err >&2)
foo
zira%

Here I get the shell prompt back immediately, which is good. But
the left-hand-side command is still running, so that it still
consumes resources; moreover, after the 3 seconds, I get

zira% err

In practice, one may want to redirect stderr to the pager too (not
always, though); this avoids this second issue, but not the first one,
which is that the left-hand-side command still consumes resources.

Does zsh provide a feature to kill the left-hand-side command in a
clean way (without a race condition, without a temporary file...)?

-- 
Vincent Lefèvre <vincent@vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

^ permalink raw reply	[flat|nested] 20+ messages in thread

end of thread, other threads:[~2019-07-30  0:41 UTC | newest]

Thread overview: 20+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
     [not found] <20190628110430.GA13790__36317.6205357135$1561719956$gmane$org@zira.vinc17.org>
2019-06-28 18:41 ` kill the LHS command of a pipe once the RHS command terminates Stephane Chazelas
2019-06-29  1:24   ` Vincent Lefevre
2019-06-29 15:30     ` Stephane Chazelas
2019-07-06 23:49       ` Vincent Lefevre
2019-07-29 23:08         ` Vincent Lefevre
2019-07-29 23:15           ` Vincent Lefevre
2019-07-29 23:42             ` Bart Schaefer
2019-07-30  0:40               ` Vincent Lefevre
2019-06-28 11:04 Vincent Lefevre
2019-06-28 11:38 ` Vincent Lefevre
2019-06-29 16:17 ` Bart Schaefer
2019-07-06 23:55   ` Vincent Lefevre
2019-07-07  4:54     ` Bart Schaefer
2019-07-09 10:08       ` Vincent Lefevre
2019-07-09 10:54         ` Vincent Lefevre
2019-07-29 15:23 ` Vincent Lefevre
2019-07-29 15:54   ` Bart Schaefer
2019-07-29 20:48     ` Vincent Lefevre
2019-07-30  0:00       ` Bart Schaefer
2019-07-30  0:17         ` Vincent Lefevre

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