Arduino, file systems, SD cards and copying

Lets say theres a file on SD card 1. I want to move it to SD card 2. Or USB thumb drive 2. Or SD Card 1 could be USB Thumb Drive 1 instead. I'm flexible. Basically the copying of one file from one serial based storage medium to another, automated.

The originating medium (SD Card 1, i.e.), ideally, would never need to be unplugged.