#! perl -slw
use strict;
use Data::Dump qw[ pp ]; $Data::Dump::WIDTH = 50;

my $reTags = join '|', map quotemeta, qw[
    HOSTNAME CONTACT TAG1 TAG2 TAG3 TAG4
];

$reTags = qr[$reTags];

my %hash = do{
    local $/;
    <DATA>
} =~ m[($reTags)=\s+(.+?)(?=$reTags|\Z)]gsm;

pp \%hash;

__DATA__
TAG1= data
TAG2= more data
HOSTNAME= fred
TAG3= even more data that sometimes has = and
runs on to more
than one line
CONTACT= Wiley Coyote
Hiesenberg Road
The Desert
TAG4= still more