Answering this question:
I would like to exclude some files during the upload tot amazon S3 (e.g. a .gitkeep file).
I see that I can use wildcars. What’s the exact syntax to exclude a bunch of file extensions ?
Wildcards can't be used to exclude extensions. Generate a list of files using the "List of files" action. Use the regular filtering actions to remove unwanted files (e.g. by filtering out particular extensions). Then use iterations to upload the remaining files to Amazon.