GNU bug report logs - #17578
cp(1) man page: behavior of "cp -R dir target" on symbolic links is unclear

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

From: Vincent Lefevre <vincent <at> vinc17.net>
To: bug-coreutils <at> gnu.org
Subject: cp(1) man page: behavior of "cp -R dir target" on symbolic links is
 unclear
Date: Sat, 24 May 2014 17:07:05 +0200

The cp(1) man page does not describe the behavior on symbolic links
when copying recursively. It appears that in such a case, cp does not
dereference the links (this is also what the info file says: "When
copying from a symbolic link, `cp' normally follows the link only
when not copying recursively."). Tested with cp (GNU coreutils) 8.21
on Debian/unstable.

As the usual behavior of utilities on symbolic links is to follow the
links, this may be surprising to the user who only reads the man page
(even if he knows POSIX, as POSIX doesn't specify the behavior if
only -R is used).

So, the man page should say that by default (e.g. without -H, -L, -P),
cp follows source symbolic links only when not copying recursively.

-- 
Vincent Lefèvre <vincent <at> vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

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

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Vincent Lefevre <vincent <at> vinc17.net>, bug-coreutils <at> gnu.org
Subject: Re: bug#17578: cp(1) man page: behavior of "cp -R dir target" on
 symbolic links is unclear
Date: Sat, 24 May 2014 10:28:30 -0700

Vincent Lefevre wrote:
> this is also what the info file says: "When
> copying from a symbolic link, `cp' normally follows the link only
> when not copying recursively."

Must be an old version; the current text says "When copying from a 
symbolic link, 'cp' normally follows the link only when not copying 
recursively or when '--link' ('-l') is used."  A bit complicated, 
unfortunately; don't know whether that detail is worth adding to the 
--help output (which the man page is derived from).

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

From: Vincent Lefevre <vincent <at> vinc17.net>
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: bug-coreutils <at> gnu.org
Subject: Re: bug#17578: cp(1) man page: behavior of "cp -R dir target" on
 symbolic links is unclear
Date: Sat, 24 May 2014 19:37:43 +0200

On 2014-05-24 10:28:30 -0700, Paul Eggert wrote:
> Vincent Lefevre wrote:
> >this is also what the info file says: "When
> >copying from a symbolic link, `cp' normally follows the link only
> >when not copying recursively."
> 
> Must be an old version;

The man page says:

GNU coreutils 8.21                April 2014                             CP(1)

April 2014, thus not that old.

-- 
Vincent Lefèvre <vincent <at> vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

Message #14 received at 17578 <at> debbugs.gnu.org (full text, mbox):

From: Bob Proulx <bob <at> proulx.com>
To: Vincent Lefevre <vincent <at> vinc17.net>
Cc: 17578 <at> debbugs.gnu.org
Subject: Re: bug#17578: cp(1) man page: behavior of "cp -R dir target" on
 symbolic links is unclear
Date: Sat, 24 May 2014 20:19:08 -0600

Vincent Lefevre wrote:
> Paul Eggert wrote:
> > Must be an old version;
> 
> The man page says:
> GNU coreutils 8.21             April 2014                    CP(1)
> April 2014, thus not that old.

On your system that must be the date when the man page was formatted.
It isn't the date when the version was released.  Version 8.21 was
released 2013-02-14 and so is now a little over a year old.

(Which I still consider relatively recent.  But a year ago recent not
a month ago recent.)

Bob

Message #17 received at 17578 <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: Vincent Lefevre <vincent <at> vinc17.net>, 17578 <at> debbugs.gnu.org
Subject: Re: bug#17578: cp(1) man page: behavior of "cp -R dir target" on
 symbolic links is unclear
Date: Sun, 25 May 2014 12:13:42 +0100

On 05/24/2014 04:07 PM, Vincent Lefevre wrote:
> The cp(1) man page does not describe the behavior on symbolic links
> when copying recursively. It appears that in such a case, cp does not
> dereference the links (this is also what the info file says: "When
> copying from a symbolic link, `cp' normally follows the link only
> when not copying recursively."). Tested with cp (GNU coreutils) 8.21
> on Debian/unstable.
> 
> As the usual behavior of utilities on symbolic links is to follow the
> links, this may be surprising to the user who only reads the man page
> (even if he knows POSIX, as POSIX doesn't specify the behavior if
> only -R is used).
> 
> So, the man page should say that by default (e.g. without -H, -L, -P),
> cp follows source symbolic links only when not copying recursively.

I suppose we could adjust --help (and thus the man page) like:

  -  -R, -r, --recursive          copy directories recursively
  +  -R, -r, --recursive          copy directories recursively (implies -P)

Message #20 received at 17578 <at> debbugs.gnu.org (full text, mbox):

From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Pádraig Brady <P <at> draigBrady.com>, 
 Vincent Lefevre <vincent <at> vinc17.net>, 17578 <at> debbugs.gnu.org
Subject: Re: bug#17578: cp(1) man page: behavior of "cp -R dir target" on
 symbolic links is unclear
Date: Sun, 25 May 2014 13:27:00 -0700

Pádraig Brady wrote:
>    -  -R, -r, --recursive          copy directories recursively
>    +  -R, -r, --recursive          copy directories recursively (implies -P)

Unfortunately it's not that simple, as -R doesn't always imply -P.

Message #23 received at 17578 <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: Paul Eggert <eggert <at> cs.ucla.edu>
Cc: 17578 <at> debbugs.gnu.org, Vincent Lefevre <vincent <at> vinc17.net>
Subject: Re: bug#17578: cp(1) man page: behavior of "cp -R dir target" on
 symbolic links is unclear
Date: Mon, 26 May 2014 09:59:04 +0100

tag 17578 wontfix
close 17578
stop

On 05/25/2014 09:27 PM, Paul Eggert wrote:
> Pádraig Brady wrote:
>>    -  -R, -r, --recursive          copy directories recursively
>>    +  -R, -r, --recursive          copy directories recursively (implies -P)
> 
> Unfortunately it's not that simple, as -R doesn't always imply -P.

Yes we shouldn't assume users would know that -H and -L would override -P.
Also --link is recently wound up in this. Hence it's not easy to describe.
We could accurately describe using something like the following, but given
that the info docs are correct and complete here and that most users use
-a anyway which already explicitly considers --no-dereference, it's probably
best to err on the side of conciseness in the man/--help and let users
refer to info for complete docs.

thanks,
Pádraig.

diff --git a/src/cp.c b/src/cp.c
index 243d6af..878266a 100644
--- a/src/cp.c
+++ b/src/cp.c
@@ -206,7 +206,8 @@ Copy SOURCE to DEST, or multiple SOURCE(s) to DIRECTORY.\n\
       --parents                use full source file name under DIRECTORY\n\
 "), stdout);
       fputs (_("\
-  -R, -r, --recursive          copy directories recursively (implies -P)\n\
+  -R, -r, --recursive          copy directories recursively. Without -H,-L or\n\
+                                 --link, implies --no-dereference\n\
       --reflink[=WHEN]         control clone/CoW copies. See below\n\
       --remove-destination     remove each existing destination file before\n\
                                  attempting to open it (contrast with --force)\

Message #30 received at 17578 <at> debbugs.gnu.org (full text, mbox):

From: Vincent Lefevre <vincent <at> vinc17.net>
To: Pádraig Brady <P <at> draigBrady.com>
Cc: Paul Eggert <eggert <at> cs.ucla.edu>, 17578 <at> debbugs.gnu.org
Subject: Re: bug#17578: cp(1) man page: behavior of "cp -R dir target" on
 symbolic links is unclear
Date: Mon, 26 May 2014 11:31:21 +0200

On 2014-05-26 09:59:04 +0100, Pádraig Brady wrote:
> Yes we shouldn't assume users would know that -H and -L would override -P.
> Also --link is recently wound up in this. Hence it's not easy to describe.

It could be described like in the info file.

> We could accurately describe using something like the following, but given
> that the info docs are correct and complete here

Not all users use the info docs (I find man / --help easier to use).

> and that most users use -a anyway which already explicitly considers
> --no-dereference,

That's the point of this bug report: I usually use -a, which implies
--no-dereference, so that I thought that -R alone would avoid this
--no-dereference, but this is not the way cp behaves.

> it's probably best to err on the side of conciseness in the
> man/--help and let users refer to info for complete docs.

That would just be one sentence below the list of options (a bit like
in the info doc).

-- 
Vincent Lefèvre <vincent <at> vinc17.net> - Web: <https://www.vinc17.net/>
100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/>
Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)

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