Replace groups.sh with groups.c.

* src/groups.c (main): New file, replacing groups.sh.
* src/group-list.c, src/group-list.h: New files, factored out of id.c,
implementing the functionality that "id" and "groups" have in common.
* src/id.c (print_full_info): Avoid a segfault when trying to print
an error message if getgroups fails.
(print_group_list): Move to group-list.c.
(print_group): Likewise.
* man/Makefile.am: When building groups.1, obtain the help text
from src/groups.c, not src/groups.sh.
(noinst_HEADERS): Add group-list.h.
(group): Remove rule.
(dist_man_MANS): Remove groups.1.
* doc/coreutils.texi (groups: Print group names a user is in):
Explain why "groups" and "groups $(id -un)" give different results
in existing login sessions after you change the group database.
(id: Print user identity): Likewise for "id".
* po/POTFILES.in: Add src/group-list.c and src/groups.c.
* NEWS: mention this.
* AUTHORS: Update.

1 files changed, 13 insertions, 1 deletions

diff --git a/doc/coreutils.texi b/doc/coreutils.texi
index dfab04001..23d0ab45b 100644
--- a/doc/coreutils.texi
+++ b/doc/coreutils.texi
@@ -12226,6 +12226,15 @@ Print only the user ID.
 
 @exitstatus
 
+@macro primaryAndSupplementaryGroups{cmd,arg}
+Primary and supplementary groups for a process are normally inherited
+from its parent and are usually unchanged since login.  This means
+that if you change the group database after logging in, @command{\cmd\}
+will not reflect your changes within your existing login session.
+Running @command{\cmd\} with a \arg\ causes the user and group
+database to be consulted afresh, and so will give a different result.
+@end macro
+@primaryAndSupplementaryGroups{id,user argument}
 
 @node logname invocation
 @section @command{logname}: Print current login name
@@ -12275,7 +12284,8 @@ options}.
 groups for each given @var{username}, or the current process if no names
 are given.  If more than one name is given, the name of each user is
 printed before
-the list of that user's groups.  Synopsis:
+the list of that user's groups and the user name is separated from the
+group list by a colon.  Synopsis:
 
 @example
 groups [@var{username}]@dots{}
@@ -12283,6 +12293,8 @@ 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}.