cp,mv: add --update=none to always skip existing files

Add --update=none which is equivalent to the --no-clobber behavior
from before coreutils 9.2.  I.e. existing files are unconditionally
skipped, and them not being replaced does not affect the exit status.

* src/copy.h [enum Update_type]: A new type to support parameters
to the --update command line option.
[enum Interactive]: Add I_ALWAYS_SKIP.
* src/copy.c: Treat I_ALWAYS_SKIP like I_ALWAYS_NO (-n),
except that we don't fail when skipping.
* src/system.h (emit_update_parameters_note): A new function
to output the description of the new --update parameters.
* src/cp.c (main): Parse --update arguments, ensuring that
-n takes precedence if specified.
(usage): Describe the new option.  Also allude that
-u is related in the -n description.
* src/mv.c: Accept the new --update parameters and
update usage() accordingly.
* doc/coreutils.texi (cp invocation): Describe the new --update
parameters.  Also reference --update from the --no-clobber description.
(mv invocation): Likewise.
* tests/mv/update.sh: Test the new parameters.
* NEWS: Mention the new feature.
Addresses https://bugs.gnu.org/62572

1 files changed, 6 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 8f947faed..e4ed291b4 100644
--- a/NEWS
+++ b/NEWS
@@ -27,6 +27,12 @@ GNU coreutils NEWS                                    -*- outline -*-
   wc will now diagnose if any total counts have overflowed.
   [This bug was present in "the beginning".]
 
+** New features
+
+  cp and mv now support --update=none to always skip existing files
+  in the destination, while not affecting the exit status.
+  This is equivalent to the --no-clobber behavior from before v9.2.
+
 
 * Noteworthy changes in release 9.2 (2023-03-20) [stable]