#include <grp.h> 

 struct group *getgrent() 

 struct group *getgrnam(name)  char *name; 

 struct group *getgrgid(gid)  gid_t gid; 

 setgroupent(stayopen)  int stayopen; 

 void setgrfile(name)  char *name; 

 setgrent() 

 void endgrent() 

struct group {
 char *gr_name; /* group name */
 char *gr_passwd; /* group password */
 gid_t gr_gid; /* group id */
 char **gr_mem; /* group members */
};

These fields are more completely described in group (5).

Getgrnam and getgrgid search the group database for a matching group name or group id, respectively, returning the first one encountered. Identical group names or group gids may result in undefined behavior.

Getgrent sequentially reads the group database and is intended for programs that wish to step through the complete list of groups.

All three routines will open the group file for reading, if necesssary.

Setgrfile changes the default group file to file , thus allowing the use of alternate group files.

Setgroupent opens the file, or rewinds it if it is already open. If stayopen is non-zero, file descriptors are left open, significantly speeding up subsequent calls. This functionality is unnecessary for 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.

Setgrent is identical to setgroupent with an argument of zero.

Endgrent closes any open files.

The routines getgrent , endgrent , setgroupent , and setgrent are fairly useless in a networked environment and should be avoided, if possible.