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.\"     From: @(#)getgrent.3	8.2 (Berkeley) 4/19/94
.\"	$Id: getgrent.3,v 1.2 1994/09/20 22:02:20 wollman Exp $
.\"
.Dd September 29, 1994
.Dt GETGRENT 3
.Os
.Sh NAME
.Nm getgrent ,
.Nm getgrnam ,
.Nm getgrgid ,
.Nm setgroupent ,
.\" .Nm setgrfile ,
.Nm setgrent ,
.Nm endgrent
.Nd group database operations
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <grp.h>
.Ft struct group *
.Fn getgrent void
.Ft struct group *
.Fn getgrnam "const char *name"
.Ft struct group *
.Fn getgrgid "gid_t gid"
.Ft struct group *
.Fn setgroupent "int stayopen"
.\" .Ft void
.\" .Fn setgrfile "const char *name"
.Ft int
.Fn setgrent void
.Ft void
.Fn endgrent void
.Sh DESCRIPTION
These functions operate on the group database file
.Pa /etc/group
which is described
in
.Xr group 5 .
Each line of the database is defined by the structure
.Ar group
found in the include
file
.Aq Pa grp.h :
.Bd -literal -offset indent
struct group {
	char	*gr_name;	/* group name */
	char	*gr_passwd;	/* group password */
	gid_t	gr_gid;		/* group id */
	char	**gr_mem;	/* group members */
};
.Ed
.Pp
The functions
.Fn getgrnam
and
.Fn getgrgid
search the group database for the given group name pointed to by
.Ar name
or the group id pointed to by
.Ar gid ,
respectively, returning the first one encountered.  Identical group
names or group gids may result in undefined behavior.
.Pp
The
.Fn getgrent
function
sequentially reads the group database and is intended for programs
that wish to step through the complete list of groups.
.Pp
All three routines will open the group file for reading, if necessary.
.Pp
The
.Fn setgroupent
function
opens the file, or rewinds it if it is already open.  If
.Fa stayopen
is non-zero, file descriptors are left open, significantly speeding
functions subsequent calls.  This functionality is unnecessary for
.Fn getgrent
as it doesn't close its file descriptors by default.  It should also
be noted that it is dangerous for long-running programs to use this
functionality as the group file may be updated.
.Pp
The
.Fn setgrent
function
is identical to
.Fn setgroupent
with an argument of zero.
.Pp
The
.Fn endgrent
function
closes any open files.
.Sh YP/NIS INTERACTION
When the
.Xr yp 4
group database is enabled, the
.Fn getgrnam
and
.Fn getgrgid
functions use the YP maps
.Dq Li group.byname
and
.Dq Li group.bygid ,
respectively, if the requested group is not found in the local
.Pa /etc/group
file.  The
.Fn getgrent
function will step through the YP map
.Dq Li group.byname
if the entire map is enabled as described in
.Xr group 5 .
.Sh RETURN VALUES
The functions
.Fn getgrent ,
.Fn getgrnam ,
and
.Fn getgrgid ,
return a pointer to the group entry if successful; if end-of-file
is reached or an error occurs a null pointer is returned.
The functions
.Fn setgroupent
and
.Fn setgrent
return the value 1 if successful, otherwise the value
0 is returned.
The functions
.Fn endgrent
and
.Fn setgrfile
have no return value.
.Sh FILES
.Bl -tag -width /etc/group -compact
.It Pa /etc/group
group database file
.El
.Sh SEE ALSO
.Fn getpwent 3 ,
.Fn group 5 ,
.Fn yp 4
.Sh HISTORY
The functions
.Fn endgrent ,
.Fn getgrent ,
.Fn getgrnam ,
.Fn getgrgid ,
and
.Fn setgrent
appeared in
.At v7 .
The functions
.Fn setgrfile
and
.Fn setgroupent
appeared in
.Bx 4.3 Reno .
.Sh COMPATIBILITY
The historic function
.Fn setgrfile ,
which allowed the specification of alternate password databases, has
been deprecated and is no longer available.
.Sh BUGS
The functions
.Fn getgrent ,
.Fn getgrnam ,
.Fn getgrgid ,
.Fn setgroupent
and
.Fn setgrent
leave their results in an internal static object and return
a pointer to that object. Subsequent calls to
the same function
will modify the same object.