How to concatenate files in AWS S3 bucket from Redshift Unload process with parallel off

Just wondering if any one has aws sdk php code to concatenate files in s3 that have been unloaded from redshift. I did use the parallel off option when unloading to try and unload to a single file, however it is limited to 6.25gb. After it reaches this limit it creates a second part and so on.

Thanks in advance