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Re: implicit redirection of background within pipeline

From: Chet Ramey
Subject: Re: implicit redirection of background within pipeline
Date: Mon, 11 Jan 2016 13:40:29 -0500
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On 1/11/16 11:37 AM, Andreas Schwab wrote:
> Chet Ramey <address@hidden> writes:
>> On 1/10/16 12:54 PM, Piotr Grzybowski wrote:
>>> hey,
>>>  I am quite sure it happens here (devel branch, at
>>> 6f82653c5ef09aeeeba4376a1c65ce86c3605c00):
>>> execute_cmd.c +5115:
>>>    if ((cmdflags & CMD_STDIN_REDIR) &&
>>>   pipe_in == NO_PIPE &&
>>>   (stdin_redirects (redirects) == 0))
>>>      async_redirect_stdin ();
>>>  but after reading the comments some 3.5k lines earlier I am not sure
>>> how to fix it; of course commenting out the if in
>>> execute_cmd.c:5112-5115 solves it, but who can tell what it breaks?
>> Posix requires this behavior:
>> "The standard input for an asynchronous list, before any explicit
>> redirections are performed, shall be considered to be assigned to a file
>> that has the same properties as /dev/null."
> But isn't it a bug that subsequent asynchronous commands in the list are
> not redirected from /dev/null?

Yes, clearly the existing behavior is inconsistent.  My response answered
Piotr's question about what it breaks.

``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    address@hidden    http://cnswww.cns.cwru.edu/~chet/

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