my $buffer = "first line\n";
foreach my $do (keys %doing) {
#    DO DB query for $do where fo $do can be serveral     bodylines;
    $buffer .= $bodyline . "\n";
}
$buffer .= "last line\n";
# now you know the file name
open FILE, ">$name" or die "bla bla";
print FILE $buffer;
close FILE;