One solution would be to convert your Excel file into a CSV or JSON file to use as a data file in Postman’s Collection Runner. You can set up a test script in the “Tests” tab of your request to verify if each file exists, and then run the collection. The Collection Runner will iterate over each entry in the data file, essentially automating the process of checking each file’s existence in your S3 bucket. After the run you can see which files exist and which do not.
That said, this solution would send a request for each file in your data file, which, with 200k files, is just not really practical or very performant.
It may be more efficient to use the AWS SDK directly with something like Python or Node