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From: Eric Blake <eblake@redhat.com>
To: Bosco <jbosco.gg@gmail.com>, dash@vger.kernel.org
Subject: Re: echo "\\1"?
Date: Thu, 27 Jul 2017 09:24:46 -0500	[thread overview]
Message-ID: <68dddf01-263e-77bd-ffc7-8e7df386ee8f@redhat.com> (raw)
In-Reply-To: <CAC4gepdsPNvUJyW4Zwto9wZGc1Naq5kMsnz+RdCyAurEZzGLZw@mail.gmail.com>


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On 07/27/2017 08:13 AM, Bosco wrote:
> On 27 July 2017 at 12:54, Eric Blake <eblake@redhat.com> wrote:
>> Which man pages?  Echo is one of those programs that varies widely, and
>> you are MUCH better off using printf(1) instead of echo(1) if you are
>> trying to get newline suppression, trying to print something that might
>> begin with -, or trying to print something that might contain \.
> 
> Sorry, maybe I did't explain it correctly, I mean the man pages of the
> dash source:
> https://git.kernel.org/pub/scm/utils/dash/dash.git/tree/src/dash.1#n1202
> 
> And because of this, I got an error compiling zziplib, you may see
> https://github.com/gdraheim/zziplib/blob/v0.13.67/configure#L17542

Eww - storing generated files in git - that forces everyone that checks
out your project to use the EXACT same version of autotools to avoid
changing the generated files unintentionally.

Looking at those lines:

>   if test -f $ac_prefix_conf_INP ; then
>     echo "s/^#undef  *\\([ABCDEFGHIJKLMNOPQRSTUVWXYZ_]\\)/#undef $ac_prefix_conf_UPP""_\\1/" > conftest.prefix

ac_prefix_conf_INP is not defined anywhere in autoconf 2.69 sources (and
you really shouldn't use the ac_ prefix if you are writing code that is
not part of autoconf proper).  I couldn't find mention of it at
https://github.com/gdraheim/zziplib/blob/v0.13.67/configure.ac, but it
may be in one of your other included files.  Can you pinpoint which part
of your configure.ac results in that part of the generated configure
file?  In all likelihood, you are using a buggy macro that is using
autoconf primitives incorrectly, and thus resulting in non-portable
code.  But without seeing the true source, I can't help you debug your
problem.

>> Arguably, since it is not required by POSIX, we don't have to do it. But
>> I also can't argue that POSIX forbids us to support \1 as an extension
>> (it says nothing about whether implementations can have additional
>> escape sequences).  So I'll argue that it is intentional as a dash
>> extension.  But if you can make dash smaller by getting rid of the
>> extension, that might be an acceptable patch.
> 
> In that case, I think, the man page of dash should be modified with
> that extension.

Indeed, or the fact that it is NOT documented means that it is an
unintentional bug for providing the extension.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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  reply	other threads:[~2017-07-27 14:24 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-27 12:23 Bosco
2017-07-27 12:54 ` Eric Blake
2017-07-27 13:13   ` Bosco
2017-07-27 14:24     ` Eric Blake [this message]
2017-07-27 14:44       ` Bosco
2017-07-27 14:51         ` Eric Blake
2017-07-27 15:10           ` Bosco
2017-07-27 15:19             ` Eric Blake
2017-07-27 15:32             ` Bosco
2017-07-27 17:26       ` Harald van Dijk

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