Magento – Best way for product export for a list of skus

The file you generated through Magento Export (whether this is default import/export module or default dataflow profile) is NOT going to work if you import it back, because it doesn't preserve the format.

If you want to update weights, I would recommend this:
1) filter your CSV in Excel, filter only those which have "sku" field assigned
2) copy-paste the filtered rows into new spreadsheet
3) leave only 2 columns - "sku", "weight"
4) import it back.

I'm pretty sure it's the easiest flow to solve your concrete task.

For those who are looking for tool for Magento that allows both export and import while having similar format for both routines, check out this one.

Meanwhile I have digged some further and it looks like more people have similar problems. Unfortunately there is nowhere a real clue why this kind of problems occur on some imports in the first place.

But there are workarounds. For the sake of completeness here two similar cases with similar workaround suggestions: Magento products not showing up after import https://stackoverflow.com/questions/12953584/product-is-not-displaying-in-listing-in-magento-after-import

Based on these threads and some other suggestions I found I now built a little PHP CLI script for my specific case which only adds the status and only when its missing:

require_once $pathToYourMagentoDirectory.'/app/Mage.php';
Mage::app();

$allProducts = Mage::getModel('catalog/product')->getCollection();
$count = 0;
foreach($allProducts as $product) {
    $currentStatus = Mage::getResourceModel('catalog/product')->getAttributeRawValue($product->getEntityId(), 'status');
    if ($currentStatus != 1 && $currentStatus != 2) {
        $product->setData('status', 1)->getResource()->saveAttribute($product, 'status');
        $count++;
    }
}
echo ('Fixed '.$count.' products by adding a valid status.');
echo ("\n");

In my case a SQL based fix like suggested in the comments above wouldn't have worked as catalog_product_entity_id simply had no entries for the newly imported products and the status attribute which could have been updated.

Still an odd problem and maybe there would be a better way to approach this - i. e. getting the initial import to work properly...