error on arch linux

[John Holland <johnbholland@icloud.com>]

getting this error on arch linux, both from the pacman version and 
compiled from source:


$ sudo  /usr/local/bin/tarsnap -c /usr/local/tarsnap-cache -f 
blowfish-etc-2026-10-26_09-12-26 /etc

tarsnap: Archive name must be specified


can't understand what's wrong. Found the error message in the source 
code but it's beyond me to understand that.