--- Begin Message ---
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Subject: |
Bug in documentation on cp |
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Date: |
Thu, 10 Oct 2013 04:02:14 +0200 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130922 Icedove/17.0.9 |
Dear Team,
I think I might have found the following bug in info cp [documentation]
The option --preserve= offers: " `links'
Preserve in the destination files any links between
corresponding source files. Note that with `-L' or `-H',
this option can convert symbolic links to hard links…
I've played around a bit, but got different results on "Note that with
`-L' or `-H', this option can convert symbolic links to hard links"
Using --preserve=links with[out] the option -H or -L I get hardlinked
files.
This happend with GNU coreutils 8.12.197-032bb.
I work on Crunchbang Linux [Debian 7], where uname -a -> 3.2.0-4-amd64
#1 SMP Debian 3.2.46-1+deb7u1 x86_64 GNU/Linux
I've posted two screenshots of this online:
with(out) the -H option: http://i.stack.imgur.com/eb8rf.png
with(out) the -L option: http://i.stack.imgur.com/U4OUV.png
In both cases, I get hard linked files - which is nice, but doesn't
accord to the documentation.
I didn't wanted to post the images as attachment because I don't know if
this is appreciated, but can transmit them if this is helpful.
I hope this helped and all the best with a hearfelt thank you for all
the good work!
A satisfied GNU/Linux user
P.S.: A short reply if this was just a misunderstanding from my side or
a real bug would be very appreciated. Thank you in advance for all your
efforts!
--- End Message ---
--- Begin Message ---
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Subject: |
Re: bug#15579: Bug in documentation on cp |
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Date: |
Thu, 10 Oct 2013 10:13:11 +0100 |
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User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2 |
On 10/10/2013 03:02 AM, hobo pope wrote:
> Dear Team,
>
>
> I think I might have found the following bug in info cp [documentation]
>
> The option --preserve= offers: " `links'
> Preserve in the destination files any links between
> corresponding source files. Note that with `-L' or `-H',
> this option can convert symbolic links to hard links…
>
> I've played around a bit, but got different results on "Note that with `-L'
> or `-H', this option can convert symbolic links to hard links"
>
> Using --preserve=links with[out] the option -H or -L I get hardlinked files.
>
> This happend with GNU coreutils 8.12.197-032bb.
>
> I work on Crunchbang Linux [Debian 7], where uname -a -> 3.2.0-4-amd64 #1 SMP
> Debian 3.2.46-1+deb7u1 x86_64 GNU/Linux
>
>
>
> I've posted two screenshots of this online:
>
> with(out) the -H option: http://i.stack.imgur.com/eb8rf.png
> with(out) the -L option: http://i.stack.imgur.com/U4OUV.png
>
> In both cases, I get hard linked files - which is nice, but doesn't accord to
> the documentation.
>
> I didn't wanted to post the images as attachment because I don't know if this
> is appreciated, but can transmit them if this is helpful.
>
> I hope this helped and all the best with a hearfelt thank you for all the
> good work!
>
>
>
>
> A satisfied GNU/Linux user
>
> P.S.: A short reply if this was just a misunderstanding from my side or a
> real bug would be very appreciated. Thank you in advance for all your efforts!
The docs are a bit terse here.
The main issue is that -a implies -d and that implies --no-dereference
which is required to get your commands to work as expected.
I.E. --no-dereference is required to stop cp implicitly
following symlinks in the source.
To verify and split out the detail being demonstrated here:
$ mkdir links; : > a; ln -s a b;
Here we see that -d overrides -H as it comes after.
Therefore we will not dereference symlinks in the first place.
$ rm links/*; cp -H -d a b links
$ l links/
lrwxrwxrwx. 1 padraig 1 Oct 10 09:37 b ▪▶ a
-rw-rw-r--. 1 padraig 0 Oct 10 09:37 a
Here we see that -H is now honored as it comes last,
and therefore symlinks are followed in the source,
resulting in hardlinks in the destination.
$ rm links/*
$ rm links/*; cp -d -H a b links
$ l links
-rw-rw-r--. 2 padraig 0 Oct 10 09:37 b
-rw-rw-r--. 2 padraig 0 Oct 10 09:37 a
I'll make the docs a bit more explicit with the following:
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index b273627..aeed4ca 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -8257,9 +8257,11 @@ $ mkdir c; : > a; ln -s a b; cp -aH a b c; ls -i1 c
@noindent
Note the inputs: @file{b} is a symlink to regular file @file{a},
yet the files in destination directory, @file{c/}, are hard-linked.
-Since @option{-a} implies @option{--preserve=links}, and since @option{-H}
-tells @command{cp} to dereference command line arguments, it sees two files
-with the same inode number, and preserves the perceived hard link.
+Since @option{-a} implies @option{--no-dereference} it would copy the symlink,
+but the later @option{-H} tells @command{cp} to dereference the command line
+arguments where it then sees two files with the same inode number.
+Then the @option{--preserve=links} option also implied by @option{-a}
+will preserve the perceived hard link.
thanks,
Pádraig.
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