Here's the documentation for the new chown/chgrp syntax:
* coreutils.texi (Disambiguating names and IDs): New section.
(chown invocation, chgrp invocation): Mention the new syntax
with an xref to the new section.
diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index ff049bc..05bf7c6 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -208,6 +208,7 @@ Common Options
* Exit status:: Indicating program success or failure.
* Backup options:: Backup options
* Block size:: Block size
+* Disambiguating names and IDs:: chgrp and chown owner and group syntax
* Random sources:: Sources of random data
* Target directory:: Target directory
* Trailing slashes:: Trailing slashes
@@ -644,6 +645,7 @@ name.
* Exit status:: Indicating program success or failure.
* Backup options:: -b -S, in some programs.
* Block size:: BLOCK_SIZE and --block-size, in some programs.
+* Disambiguating names and IDs:: chgrp and chown owner and group syntax
* Random sources:: --random-source, in some programs.
* Target directory:: Specifying a target directory, in some
programs.
* Trailing slashes:: --strip-trailing-slashes, in some programs.
@@ -924,6 +926,46 @@ set. The @option{-h} or @option{--human-readable} option
is equivalent to
@option{--block-size=human-readable}. The @option{--si} option is
equivalent to @option{--block-size=si}.
[EMAIL PROTECTED] Disambiguating names and IDs
[EMAIL PROTECTED] chown and chgrp: Disambiguating user names and IDs
[EMAIL PROTECTED] user names, disambiguating
[EMAIL PROTECTED] user IDs, disambiguating
[EMAIL PROTECTED] group names, disambiguating
[EMAIL PROTECTED] group IDs, disambiguating
[EMAIL PROTECTED] disambiguating group names and IDs
+
+Since the @var{owner} and @var{group} arguments to @command{chown} and
[EMAIL PROTECTED] may be specified as names or numeric IDs, there is an
+apparent ambiguity.
+What if a user or group @emph{name} is a string of digits?
[EMAIL PROTECTED] a number as a user name is common in some environments.}
+Should the command interpret it as a user name or as an ID?
[EMAIL PROTECTED] requires that @command{chown} and @command{chgrp}
+first attempt to resolve the specified string as a name, and
+only once that fails, then try to interpret it as an ID.
+This is troublesome when you want to specify a numeric ID, say 42,
+and it must work even in a pathological situation where
[EMAIL PROTECTED] is a user name that maps to some other user ID, say 1000.
+Simply invoking @code{chown 42 F}, will set @file{F}s owner ID to
+1000---not what you intended.
+
+GNU @command{chown} and @command{chgrp} provide a way to work around this,
+that at the same time may result in a significant performance improvement
+by eliminating a database look-up.
+Simply precede each numeric user ID and/or group ID with a @samp{+},
+in order to force its interpretation as an integer:
+
[EMAIL PROTECTED]
+chown +42 F
+chgrp +$numeric_group_id another-file
+chown +0:+0 /
[EMAIL PROTECTED] example
+
+GNU @command{chown} and @command{chgrp}
+skip the name look-up process for each @samp{+}-prefixed string,
+because a string containing @samp{+} is never a valid user or group name.
+This syntax is accepted on most common Unix systems, but not on Solaris 10.
+
@node Random sources
@section Sources of random data
@@ -8778,6 +8820,10 @@ owner nor the group is changed.
@end table
+If @var{owner} or @var{group} is intended to represent a numeric user
+or group ID, then you may specify it with a leading @samp{+}.
[EMAIL PROTECTED] names and IDs}.
+
Some older scripts may still use @samp{.} in place of the @samp{:} separator.
@acronym{POSIX} 1003.1-2001 (@pxref{Standards conformance}) does not
require support for that, but for backward compatibility @acronym{GNU}
@@ -8953,6 +8999,10 @@ or to the group of an existing reference file. Synopsis:
chgrp [EMAIL PROTECTED]@dots{} @[EMAIL PROTECTED] | [EMAIL PROTECTED]@}
@[EMAIL PROTECTED]
@end example
+If @var{group} is intended to represent a
+numeric group ID, then you may specify it with a leading @samp{+}.
[EMAIL PROTECTED] names and IDs}.
+
The program accepts the following options. Also see @ref{Common options}.
@table @samp
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