This is a Magento 1 script, it won’t work for Magento 2.
The script will loop through a CSV file and update the SKU on each product. This can be useful when a website owner changes supplier or when they hook their Magento store up to a CRM which requires specific SKUs to be used.
Place the following script in your Magento root folder
First create your CSV with the old and new SKU numbers in a simple CSV file as follows and upload onto FTP into the magento/var/import directory.
1232,new-24B8 442,2w39489 0909d,11299033
One product on each line the current SKU followed by a comma, then the new SKU you wanto to use followed by a new line. Next, place the following script in the root folder of your Magento install. Make sure $updates_file matches the location of the CSV file on the server.
An alternative method uses the SOAP API built into Magento but is slightly slower.