Description

   The getegid function can be used with POSIX style identifiers
   (IDs) or with UIC-based identifiers.

   POSIX style IDs are supported on OpenVMS Version 7.3-2 and
   higher.

   With POSIX style IDs disabled, the getegid and getgid functions
   are equivalent and return the group number from the current UIC.
   For example, if the UIC is [313,031], 313 is the group number.

   With POSIX style IDs enabled, getegid returns the effective group
   ID of the calling process, and getgid returns the real group ID
   of the calling process. The real group ID is specified at login
   time. The effective group ID is more transient, and determines
   additional access permission during execution of a set-group-ID
   process. It is for such processes that the getgid function is
   most useful.

   The getegid function is always successful; no return value is
   reserved to indicate an error.

   See also geteuid and getuid.