id: add -z, --zero option

* src/group-list.h (print_group_list): Add a parameter for the
delimiter of type char.
* src/group-list.c (print_group_list): Likewise, and use it instead
of a white space character to delimit the group entries.
* src/groups.c (main): Pass white space character to print_group_list().
* src/id.c (longopts):  Add array element for the new long option.
(usage): Document the new option.  While at it, fix the alignment
of the descriptions to match that of HELP_OPTION_DESCRIPTION.
(main): Define the bool flag opt_zero indicating the use of the
new option.  In the getopt_long loop, handle it.
Output an error diagnostic in the case the --zero option has been
specified together with the default format.
In the case of -gG, pass either a NUL or a white space character to
print_group_list() - depending on the above new flag.
Likewise change the printing of the final newline character: output
a NUL instead if the --zero option has been specified.
* doc/coreutils.texi (id invocation): Document the new option.
While at it, move the @exitstatus macro down after the macro
@primaryAndSupplementaryGroups in order to be consistent with
other texinfo documents.
(groups invocation): Move @exitstatus down after the macro
@primaryAndSupplementaryGroups here, too.
* tests/misc/id-zero.sh: Add new test exercising the new option.
* tests/local.mk (all_tests): Reference it.
* NEWS (New features): Mention the new option.
Fixes http://bugs.gnu.org/9987

1 files changed, 17 insertions, 5 deletions

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index 21216b4be..d022c4560 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -14516,9 +14516,20 @@ Print only the security context of the current user.
 If SELinux is disabled then print a warning and
 set the exit status to 1.
 
-@end table
+@item -z
+@itemx --zero
+@opindex -z
+@opindex --zero
+Delimit output items with NUL characters.
+This option is not permitted when using the default format.
 
-@exitstatus
+Example:
+@example
+$ id -Gn --zero
+users <NUL> devs <NUL>
+@end example
+
+@end table
 
 @macro primaryAndSupplementaryGroups{cmd,arg}
 Primary and supplementary groups for a process are normally inherited
@@ -14530,6 +14541,8 @@ database to be consulted afresh, and so will give a different result.
 @end macro
 @primaryAndSupplementaryGroups{id,user argument}
 
+@exitstatus
+
 @node logname invocation
 @section @command{logname}: Print current login name
 
@@ -14587,13 +14600,12 @@ groups [@var{username}]@dots{}
 
 The group lists are equivalent to the output of the command @samp{id -Gn}.
 
-@primaryAndSupplementaryGroups{groups,list of users}
-
 The only options are @option{--help} and @option{--version}.  @xref{Common
 options}.
 
-@exitstatus
+@primaryAndSupplementaryGroups{groups,list of users}
 
+@exitstatus
 
 @node users invocation
 @section @command{users}: Print login names of users currently logged in