How to get a password hash through terminal in Recovery Mode?
You didn't specify a special macOS version but at least in Sierra it can be done by:


open Terminal.app in the menubar > Utilities
get the name of the main system volume with diskutil list (e.g. Macintosh HD)
enter in Terminal:

defaults read /Volumes/&lt;volume_name&gt;/var/db/dslocal/nodes/Default/users/&lt;user_name&gt;.plist ShadowHashData|tr -dc 0-9a-f|/Volumes/&lt;volume_name&gt;/usr/bin/xxd -r -p|/Volumes/&lt;volume_name&gt;/usr/bin/plutil -convert xml1 - -o -


Example (with the main system volume name Macintosh HD and the user name user272783):

defaults read /Volumes/Macintosh\ HD/var/db/dslocal/nodes/Default/users/user272783.plist ShadowHashData|tr -dc 0-9a-f|/Volumes/Macintosh\ HD/usr/bin/xxd -r -p|/Volumes/Macintosh\ HD/usr/bin/plutil -convert xml1 - -o -


If you specify a file name and choose a r/w volume as destination drive, you can write the file to a volume (... -o /Volumes/FlashDrive/user272783.plist)




Please check: What type of hash are a Mac's password stored in?