Safe removal of flash disk

In Ubuntu 16.04, I try to safely remove the flash disk from the command line. When I run the following script (from the https://unix.stackexchange.com/questions/178638/eject-safely-remove-vs-umount) : udisksctl unmount -b /dev/sdb1 udisksctl power-off -b /dev/sdb1 It says: Error powering off drive: Error opening /sys/devices/pci0000:00/0000:00:1a.0/usb1/1-1/1-1.1/remove: No such file or directory (udisks-error-quark, 0) When I type these commands from the keyboard, I don't get the error. Why, and how should I make the script running?