#!/bin/sed -f
# Echo stdin with:
#	comments removed;
#	initial and terminal whitespace removed;
#	whitespace strings replaced by single blanks;
#	leading zeroes removed from nameserver address fields;
#	first set of zero fields in an IPv6 address collapsed to '::';
#	empty lines removed.
s/#.*$//
s/[[:blank:]]\+$//
s/^[[:blank:]]\+//
s/[[:blank:]]\+/ /g
/^nameserver/!b ENDOFCYCLE
s/$/ /
s/\([:. ]\)0\+/\10/g
s/\([:. ]\)0\([123456789abcdefABCDEF][[:xdigit:]]*\)/\1\2/g
/::/b ENDOFCYCLE; s/ \(0[: ]\)\+/ ::/
/::/b ENDOFCYCLE; s/:\(0[: ]\)\+/::/
: ENDOFCYCLE

s/[[:blank:]]\+$//
/^$/d