Command from here
https://android.stackexchange.com/a/78183/239063
From a command line run
( printf "\x1f\x8b\x08\x00\x00\x00\x00\x00" ; tail -c +25 ~/Path/to/android_backup.ab ) | tar xfvz -
Command from here
https://android.stackexchange.com/a/78183/239063
From a command line run
( printf "\x1f\x8b\x08\x00\x00\x00\x00\x00" ; tail -c +25 ~/Path/to/android_backup.ab ) | tar xfvz -