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.Dd April 19, 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 int
.Fn setgroupent "int stayopen"
.\" .Ft void
.\" .Fn setgrfile "const char *name"
.Ft void
.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
.Li struct 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
.Fa name
or the group ID pointed to by
.Fa gid ,
respectively, returning the first one encountered.  Identical group
names or group GIDs may result in undefined behavior.
.Pp
.Fn getgrent
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
.Fn setgroupent
opens the file, or rewinds it if it is already open.  If
.Fa stayopen
is non-zero, file descriptors are left open, significantly speeding
subsequent function 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
.Fn setgrent
is equivalent to
.Fn setgroupent
with an argument of zero.
.Pp
The
.Fn endgrent
function
closes any open files.
.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
.Fn setgroupent
function returns the value 1 if successful, otherwise 0.
The 
.Fn endgrent
and
.Fn setgrent
functions have no return value.
.Sh FILES
.Bl -tag -width /etc/group -compact
.It Pa /etc/group
group database file
.El
.Sh SEE ALSO
.Xr getpwent 3 ,
.Xr group 5
.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
.Xr setgrfile 3 ,
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.
.Pp
The functions
.Fn getgrent ,
.Fn endgrent ,
.Fn setgroupent ,
and
.Fn setgrent
are fairly useless in a networked environment and should be
avoided, if possible.