Why am I receiving no response from s3cmd command from php?

I was able to find a possible solution on this discussion on StackOverflow, where the user was able to resolve the issue by using the full path. Be sure you update the below command with your correct information:

exec('/usr/local/bin/s3cmd --access_key=ZZZZZ --secret_key=XXXXX put /Users/me/filename.jpg s3://bucketname/foldername/'); 

I hope this helps resolve the issue.