local $/ = ",";

my $dn = "";
while(<>) {
    my $complete_dn;

    if(m/ \A (.+ = .+) \n ( \w+ = .+ ,) \z /sx) {
        $complete_dn = $dn . $1;
        $dn = $2;
    }
    else {
        $dn .= $_;
    }

    if($_ = $complete_dn) {
        s/\n+//g;
        print $_, "\n";
    }
}