File Pre- and Post-Processing (Prepost) HST Server can run file processing scripts that run before or after a transfer session or file transfer. Setting Up Pre/Post Processing HST Server can be configured to run scripts that are triggered by session start, session stop, file start, and file stop. Pre/Post Variables HST Server supports an extensive set of variables that can be used in prepost scripts. Pre/Post Script Examples The following pre-processing and post-processing script examples demonstrate how Aspera prepost environment variables are used to achieve different types of processing.