Arduino and Host shileds

Can anyone provide codes to transfer files from and to a "Pendrive" using arduino and arduino us host shileds?

There is a lot documentation for the USB host Shield, see : https://www.arduino.cc/en/Main/ArduinoUSBHostShield
The normal Arduino boards are not a computer and can not transfer files from one USB flash drive to another. The Arduino Yun contains a wifi/linux/OpenWRT module which can do that.