use Modern::Perl;
use String::Trim;
use Data::Dumper;
$Data::Dumper::Sortkeys = 1;
$Data::Dumper::Terse    = 1;

my @rows;
while (<DATA>)
{
	chomp;
	trim;
	
	my @F = split /\s*=\s*/;
	
	push @rows, [map {
		my %x = (field => $F[$_ - 1], value => $F[$_]);
		$x{field} =~ s/.*\s+(\S+)$/$1/ unless $_ == 1;
		$x{value} =~ s/\s*\S+$// unless $_ == $#F;
		\%x;
	} 1 .. $#F];
}

print Dumper \@rows;

for (@rows)
{
	say join q(,), map { $_->{value} } @$_;
}

__DATA__
FIELDA = ONEAL FIELDB = RELAY FIELDC = L1208 FIELDD = ALTS
FIELDA = OSSIPEE FIELDB = DISC FIELDC = SOH: 169879251 FIELDD = DISC
FIELDA = OSSIPEE FIELDB = RELAY FIELDC = L1201 FIELDD = ALTS
FIELDA = OSSIPEE FIELDB = RELAY FIELDC = L1203 FIELDD = ALTS