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From: Vincent Lefevre <vincent@vinc17.net>
To: zsh-users@zsh.org
Subject: Re: detect pipe
Date: Sun, 14 Feb 2021 22:19:22 +0100	[thread overview]
Message-ID: <20210214211922.GA2302738@zira.vinc17.org> (raw)
In-Reply-To: <CAH+w=7Y=3osi+0LHadHAdEQVyPWHsX0a5V2iZGCdSE3VF0=E8w@mail.gmail.com>

On 2021-02-14 11:33:11 -0800, Bart Schaefer wrote:
> On Sun, Feb 14, 2021 at 9:31 AM Vincent Lefevre <vincent@vinc17.net> wrote:
> > Closing stdin is a bad idea, as this can break stdout redirection,
> > and this may be out of control of the commands. See
> >
> >   https://sourceware.org/bugzilla/show_bug.cgi?id=682
> 
> IMO that's just silly.  If stdin/stdout were never supposed to be
> closed, why has the standard shell had <&- and >&- for its entire
> existence?  Why wouldn't those be syntax errors when a file descriptor
> number is not provided if you're never supposed to use them?

To make the rule the same for all file descriptors and all redirection
type?

Note also that something like

  { cat < file } <&-

is OK (the <&- is useless here, but there might be cases where this
could be useful).

In any case, it is a bad idea to use a closed standard fd, unless
you know that this is supported by the command. For instance, note
the difference with "cat" from the GNU coreutils 8.32:

$ echo foo > file
$ cat <&- file -
foo
cat: -: Bad file descriptor
cat: closing standard input: Bad file descriptor
$ cat < /dev/null file -
foo
$ 

-- 
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)


  parent reply	other threads:[~2021-02-14 21:19 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-27 16:45 Ray Andrews
2021-01-27 23:59 ` Bart Schaefer
2021-01-28  4:57   ` Ray Andrews
2021-01-28  6:16     ` Bart Schaefer
2021-01-28 10:08     ` Vincent Lefevre
2021-01-28 10:28       ` Vincent Lefevre
2021-01-28 15:05         ` Ray Andrews
2021-01-28 15:45           ` Ray Andrews
2021-01-28 20:58             ` Bart Schaefer
2021-01-28 20:59               ` Bart Schaefer
2021-01-29  1:17               ` Ray Andrews
2021-01-29  2:50                 ` Bart Schaefer
2021-01-29  3:21                   ` Ray Andrews
2021-01-30  0:29                     ` Bart Schaefer
2021-01-30 14:26                       ` Ray Andrews
2021-01-30 19:00                         ` Bart Schaefer
2021-01-30 19:19                           ` Ray Andrews
2021-01-31 19:12                             ` Ray Andrews
2021-01-31 21:28                               ` Bart Schaefer
2021-02-14 17:31                           ` Vincent Lefevre
2021-02-14 19:33                             ` Bart Schaefer
2021-02-14 20:33                               ` Ray Andrews
2021-02-14 21:20                                 ` Bart Schaefer
2021-02-14 22:25                                   ` Ray Andrews
2021-02-14 21:24                                 ` Vincent Lefevre
2021-02-14 21:19                               ` Vincent Lefevre [this message]
2021-02-14 21:24                                 ` Bart Schaefer
2021-02-14 21:38                                 ` Bart Schaefer

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