Unfortunately, s3cmd cannot delete files with a wildcard. You cannot just
s3cmd del s3://my-bucket/*
Well, you can, s3cmd will also report "Object * deleted" but all your files stay in the bucket!
I know why guys in Amazon decided to do so but that is a long story, let's go back to practice.
I suggest a unix-way here (well, I would suggest it anyway):
s3cmd ls s3://my-bucket/ | awk '{print $4}' | xargs s3cmd del
That is all, You will get list of files in an output.
Another way, is to "s3cmd sync" your bucket against an empty directory
