dave@rpi5:~ $ git clone https://github.com/adafruit/Adafruit-Pi-ExternalRoot-Helper.git
Cloning into 'Adafruit-Pi-ExternalRoot-Helper'...
remote: Counting objects: 53, done.
remote: Total 53 (delta 0), reused 0 (delta 0), pack-reused 53
Unpacking objects: 100% (53/53), done.
Checking connectivity... done.

dave@rpi5:~/Adafruit-Pi-ExternalRoot-Helper $ sudo su -
[sudo] password for dave: 
root@rpi5:~# cd ~dave/Adafruit-Pi-ExternalRoot-Helper/
root@rpi5:/home/dave/Adafruit-Pi-ExternalRoot-Helper# ./adafruit-pi-externalroot-helper -d /dev/sda
Target drive = /dev/sda
[start] Will create new ext4 filesystem on /dev/sda
[start] If there is data on /dev/sda, it will be lost.
Really proceed? (y)es / (n)o y
[dependencies] Installing gdisk, rsync, and parted.
Reading package lists... Done
Building dependency tree       
Reading state information... Done
parted is already the newest version.
rsync is already the newest version.
rsync set to manually installed.
The following NEW packages will be installed:
  gdisk
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 193 kB of archives.
After this operation, 799 kB of additional disk space will be used.
Do you want to continue? [Y/n] 
Get:1 http://mirrordirector.raspbian.org/raspbian/ jessie/main gdisk armhf 0.8.10-2 [193 kB]
Fetched 193 kB in 0s (321 kB/s)
Selecting previously unselected package gdisk.
(Reading database ... 127195 files and directories currently installed.)
Preparing to unpack .../gdisk_0.8.10-2_armhf.deb ...
Unpacking gdisk (0.8.10-2) ...
Processing triggers for man-db (2.7.0.2-5) ...
Setting up gdisk (0.8.10-2) ...
[fs create] Creating /dev/sda1
[fs create] Creating ext4 filesystem on /dev/sda1
mke2fs 1.42.12 (29-Aug-2014)
Creating filesystem with 29304832 4k blocks and 7331840 inodes
Filesystem UUID: 08fcdeb6-7df7-4aeb-a21b-c48438cfb828
Superblock backups stored on blocks: 
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
        4096000, 7962624, 11239424, 20480000, 23887872

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done   

[fs id] Getting UUID for target partition
[fs id] Getting Partition unique GUID for target filesystem
[fs id] Target partition UUID: 08fcdeb6-7df7-4aeb-a21b-c48438cfb828
[fs id] Partition unique GUID: 6F8E0B29-6C85-490F-A316-1092BC2A7D86
[fs copy] Mounting /dev/sda1 on /mnt
[fs copy] Copying root filesystem to /dev/sda1 with rsync
[fs copy] This will take quite a while.  Please be patient!
[boot config] Configuring boot from {/dev/sda1}
[boot config] Commenting out old root partition in /etc/fstab, adding new one
[boot config] Ok, your system should be ready. You may wish to check:
[boot config]   /mnt/etc/fstab
[boot config]   /boot/cmdline.txt
[boot config] Your new root drive is currently accessible under /mnt.
[boot config] In order to restart with this drive at /, please type:
[boot config] sudo reboot