my @columns = qw(
    Field_1
    Field_2
    Field_3
);

my $flush = $columns[-1]; # maybe you have a better way of knowing when your set is complete

# output header:
print join("\t", @columns), "\n";

my %row;
while (<>) {
    if (/(\w+) = (.*)/) {
       $row{ $1 } = $2;
       if ($1 eq $flush) {
           print join("\t", @row{ @columns }),"\n";
       };
    } else {
       warn "Unknown line: $_";
       next;
    };
};