Upload External File to Drupal File System
Take a look at foldershare and foldershare_rest modules, they provide entire data management pipeline on a Drupal site, along with a ready to use rest client cum command line utility. Here are couple videos that show the module's capabilities

Managing data via REST client for automation and power users (5 mins)
Managing data on SeedMeLab for users(3mins)

Disclosure: I am the maintainer for these modules.