ifconfig(8): make it possible to filter output by interface group.
Now options -g/-G allow to select/unselect interfaces by groups
in the "ifconfig -a" output just like already existing -d/-u.
Examples:
to exclude loopback from the list: ifconfig -a -G lo
to show vlan interfaces only: ifconfig -a -g vlan
to show tap interfaces that are up: ifconfig -aug tap
Arguments to -g/-G may be shell patterns and both may be specified.
Later options -g/-G override previous ones.