Re: semantics of cp -R

[Paul Eggert]

address@hidden writes:

> $ mkdir c
> $ ln -s c a
> $ cp -RPv a b
> `a' -> `b'
> $ cp -RPv a b
> `a' -> `b/a'
>
> violates POSIX by my reading, since the target 'b' exists and is of type
> symlink (not directory).

The POSIX spec says that the -P option affects a "symbolic link
specified as a source_file operand or any symbolic link encountered
during traversal of a file hierarchy".  I interpret the last part
of this phrase to be talking about traversal of the source_file
hierarchy.  If so, the -P option should not affect whether "b"
is dereferenced in the early step (before step 1) where
POSIX says

  If target exists and is a file of type directory, the name of the
  corresponding destination path for each file in the file hierarchy
  shall be the concatenation of target, a slash character, and the
  pathname of the file relative to the directory containing
  source_file.

Here, the target b is a symbolic link to a directory; does this count
as a directory?  Traditionally I think the answer is "yes".

> Is this a bug in coreutils, or a weakness in the POSIX specification that
> needs to be brought up to the Open Group?

The spec could be clearer, yes.

> I also found it odd that the --no-dereference option (-n in ln, -P in cp)
> behaves differently:

The --no-dereference option is in a bit of a wierd state, I'm afraid.
It's been on my list of things to look at for a several months now,
but I haven't have the time to spend on it.  Please see
<http://lists.gnu.org/archive/html/bug-coreutils/2004-05/msg00140.html>
for some thoughts (but they're not all correct :-).

> I already showed that cp -P dereferences a destination symlink to a
> directory, even though the similar ln -n does not.  Maybe it would make
> sense for cp to have:
> -n --no-target-dereference   Don't dereference target
> -P --no-source-dereference   Don't dereference sources
> --no-dereference             Same as -nP

An interesting idea...

> My intent was to do something like:
> LIST='foo_file bar_dir blah/my_file blah/my_dir'
> SRC=src
> DST=dst
> CP='ln -sn'
> for file in $LIST; do
>   $CP ${SRC}/$file ${DST}/$file
> done

Have you looked into the new --no-target-directory (-T) option?  It
would appear to do what you want.  It's in CVS coreutils.