Subject: Re: bug#34488: Add sort --limit, or document workarounds for sort|head error messages

From: Eric Blake <[email-masked]>
Date: Mon, 18 Feb 2019 10:02:40 -0600

On 2/17/19 8:20 PM, Pádraig Brady wrote:
> On 15/02/19 07:20, Eric Blake wrote:
>> Except that POSIX has the nasty requirement that sh started with an
>> inherited ignored SIGPIPE must silently ignore all attempts from within
>> the shell to restore SIGPIPE handling to child processes of the shell:
>>
>> $ (trap '' PIPE; bash -c 'trap - PIPE; \
>>    seq 9999 | sort -n | sed 5q | wc -l')
>> 5
>> sort: write failed: 'standard output': Broken pipe
>> sort: write error
> 
>> You HAVE to use some other intermediate program if you want to override
>> an inherited ignored SIGPIPE in sh into an inherited default-behavior
>> SIGPIPE in sort.
> 
> Should we also propose to POSIX to allow trap to specify default?

That's what "trap - PIPE" is already supposed to do, except that POSIX
has the odd requirement that a signal that was inherited ignored cannot
be reset to default.

> Maybe `trap 0 PIPE` or similar?

Alas, bash has already defined that to mean the same as 'trap - EXIT PIPE'.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
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