GNU bug report logs - #34026
doc: explain long-vs-short options

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>
To: bug-coreutils <at> gnu.org
Subject: mention that long options aren't always as good as short options
Date: Thu, 10 Jan 2019 09:47:38 +0800

On (info "(coreutils) Common options")
mention that, though clearer, long options aren't always as good as short options,
$ touch --reference=~jidanni/.pcmanx /cf/pcmanx_time
touch: failed to get attributes of '~jidanni/.pcmanx/pcmanx': No such file or directory
Unless one removes the '=':
$ touch --reference ~jidanni/.pcmanx/pcmanx /cf/pcmanx_time
$
(due to the shell helping out with "~...")

Message #8 received at 34026 <at> debbugs.gnu.org (full text, mbox):

From: Eric Blake <eblake <at> redhat.com>
To: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>,
 34026 <at> debbugs.gnu.org
Subject: Re: bug#34026: mention that long options aren't always as good as
 short options
Date: Wed, 9 Jan 2019 22:10:55 -0600

[Message part 1 (text/plain, inline)]

On 1/9/19 7:47 PM, 積丹尼 Dan Jacobson wrote:
> On (info "(coreutils) Common options")
> mention that, though clearer, long options aren't always as good as short options,
> $ touch --reference=~jidanni/.pcmanx /cf/pcmanx_time
> touch: failed to get attributes of '~jidanni/.pcmanx/pcmanx': No such file or directory
> Unless one removes the '=':
> $ touch --reference ~jidanni/.pcmanx/pcmanx /cf/pcmanx_time
> $
> (due to the shell helping out with "~...")

The same is true for short options: 'touch -rfile' and 'touch -r file'
are almost identical, except for 'touch -r~file' and 'touch -r ~file'.
So it is NOT a case of long options not being as good as short options.

Note that bash defaults to doing ~ expansion after =, but that this is a
bash extension and is disabled by default when bash is in POSIX mode.
But not even bash can tell that you want tilde expansion if you write
the argument of a short option adjacent to the option rather than as a
separate argument.  So in _that_ regards, if you want to pass as small
of an argv[] as possible, the long option form with = is BETTER than the
short option form of concatenation, if you use bash as your shell.

Spelling long options with a space instead of = is fine for all long
options that have a mandatory option, and we try to avoid long options
with optional arguments (where you have to use =).  That said, I agree
that having some mention in the manual of the effects of =~ having
different behaviors depending on the shell would be helpful.  Remember,
if you want tilde expansion it is best to present that option argument
as a standalone argument so that the tilde starts the word; when that is
not possible (such as for the less common case of an optional argument
to a long option), you can use $HOME/ instead of ~/, or else have to
resort to a temporary variable to perform the tilde expansion
separately, as in:

tmp=~user; touch --reference=$tmp/.pcmanx/pcmanx /cf/pcmanx_time

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

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Message #11 received at 34026 <at> debbugs.gnu.org (full text, mbox):

From: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>
To: Eric Blake <eblake <at> redhat.com>
Cc: 34026 <at> debbugs.gnu.org
Subject: Re: bug#34026: mention that long options aren't always as good as
 short options
Date: Thu, 10 Jan 2019 12:23:44 +0800

Yes do warn in the manual, as here root (so no $HOME) expected tilde
expansion... Thanks.

Message #14 received at 34026 <at> debbugs.gnu.org (full text, mbox):

From: Assaf Gordon <assafgordon <at> gmail.com>
To: 積丹尼 Dan Jacobson <jidanni <at> jidanni.org>,
 Eric Blake <eblake <at> redhat.com>
Cc: 34026 <at> debbugs.gnu.org
Subject: Re: bug#34026: mention that long options aren't always as good as
 short options
Date: Fri, 11 Jan 2019 01:31:16 -0700

severity 34026 wishlist
retitle 34026 doc: explain long-vs-short options
stop

Hello,

On 2019-01-09 9:23 p.m., 積丹尼 Dan Jacobson wrote:
> Yes do warn in the manual, as here root (so no $HOME) expected tilde
> expansion... Thanks.

I'm marking this as a wish-list item.

If we are to add a section dedicated to options parsing,
it's worth noting related discussion about using two dashes
to stop processing ( http://bugs.gnu.org/33942 ),
and some similar section in the guile manual:
https://www.gnu.org/software/guile/manual/html_node/Command-Line-Format.html

regards,
 - assaf

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