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, 26 insertions, 2 deletions

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 7852e9f8a..2188922c6 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -9236,9 +9236,9 @@ results in an error message on systems that do not support symbolic links.
 @optNoTargetDirectory
 
 @item -u
-@itemx --update
+@itemx --update[=@var{which}]
 @opindex -u
-@opindex --update
+@opindex --update[=@var{which}]
 @cindex newer files, copying only
 Do not copy a non-directory that has an existing destination with the
 same or newer modification timestamp; instead, silently skip the file
@@ -9254,6 +9254,26 @@ for example), that will take precedence; consequently, depending on the
 order that files are processed from the source, newer files in the destination
 may be replaced, to mirror hard links in the source.
 
+@macro whichUpdate
+@var{which} gives more control over which existing files in the
+destination are replaced, and its value can be one of the following:
+
+@table @samp
+@item all
+This is the default operation when an @option{--update} option is not specified,
+and results in all existing files in the destination being replaced.
+
+@item none
+This is similar to the @option{--no-clobber} option, in that no files in the
+destination are replaced, but also skipping a file does not induce a failure.
+
+@item older
+This is the default operation when @option{--update} is specified, and results
+in files being replaced if they're older than the corresponding source file.
+@end table
+@end macro
+@whichUpdate
+
 @item -v
 @itemx --verbose
 @opindex -v
@@ -10165,6 +10185,8 @@ of its permissions, and fail if the response is not affirmative.
 Do not overwrite an existing file; silently fail instead.
 @mvOptsIfn
 This option is mutually exclusive with @option{-b} or @option{--backup} option.
+See also the @option{--update=none} option which will
+skip existing files but not fail.
 
 @item --no-copy
 @opindex --no-copy
@@ -10188,6 +10210,8 @@ same source and destination.
 This option is ignored if the @option{-n} or @option{--no-clobber}
 option is also specified.
 
+@whichUpdate
+
 @item -v
 @itemx --verbose
 @opindex -v