New option --no-dereference.

* src/diff.h (no_dereference_symlinks): New variable.
* src/diff.c: Include xreadlink.h.
(longopts): Add --no-dereference option.
(main): Accept --no-dereference option.
(option_help_msgid): Mention the --no-dereference option.
(compare_files): If no_dereference_symlinks is true, use lstat()
instead of stat(). Compare symbolic links by comparing their values.
* bootstrap.conf (gnulib_modules): Add lstat, stat, xreadlink.
* doc/diffutils.texi (Comparing Directories, diff Options): Mention the
--no-dereference option.
* tests/no-dereference: New file.
* tests/Makefile.am (TESTS): Add it.

1 files changed, 10 insertions, 0 deletions

diff --git a/doc/diffutils.texi b/doc/diffutils.texi
index 5aff3c3..58b140c 100644
--- a/doc/diffutils.texi
+++ b/doc/diffutils.texi
@@ -1846,6 +1846,13 @@ is specified while the @option{--ignore-file-name-case} option is in
 effect, case is ignored when excluding file names matching the
 specified patterns.
 
+To avoid that @command{diff} follows symbolic links, use the
+@c later: @option{--no-dereference} (@option{-P}).
+@option{--no-dereference}.
+When this option is in use,
+symbolic links will be treated like a special kind of files, rather than
+comparing the target of each symbolic link.
+
 @node Adjusting Output
 @chapter Making @command{diff} Output Prettier
 
@@ -3848,6 +3855,9 @@ file in if-then-else format.  @xref{Line Group Formats}.
 Use @var{format} to output a line taken from just the second file in
 if-then-else format.  @xref{Line Formats}.
 
+@item --no-dereference
+Act on symbolic links themselves instead of what they point to.
+
 @item --old-group-format=@var{format}
 Use @var{format} to output a group of lines taken from just the first
 file in if-then-else format.  @xref{Line Group Formats}.