=over

=item $EFFECTIVE_GROUP_ID

=item $EGID

=item $)
X<$)> X<$EGID> X<$EFFECTIVE_GROUP_ID>

The effective gid of this process.  If you are on a machine that
supports membership in multiple groups simultaneously, gives a space
separated list of groups you are in.  The first number is the one
returned by C<getegid()>, and the subsequent ones by C<getgroups()>,
one of which may be the same as the first number.

Similarly, a value assigned to C<$)> must also be a space-separated
list of numbers.  The first number sets the effective gid, and
the rest (if any) are passed to C<setgroups()>.  To get the effect of an
empty list for C<setgroups()>, just repeat the new effective gid; that is,
to force an effective gid of 5 and an effectively empty C<setgroups()>
list, say C< $) = "5 5" >.

You can change both the effective gid and the real gid at the same
time by using C<POSIX::setgid()> (use only a single numeric argument).
Changes to C<$)> require a check to C<$!> to detect any possible errors
after an attempted change.

C<< $< >>, C<< $> >>, C<$(> and C<$)> can be set only on
machines that support the corresponding I<set[re][ug]id()> routine.  C<$(>
and C<$)> can be swapped only on machines supporting C<setregid()>.

Mnemonic: parentheses are used to I<group> things.  The effective gid
is the group that's I<right> for you, if you're running setgid.

=back