ANSWER:

./nz c a -cc file.nz files/*
Unknown command c

I assume you actually did something like

./nz a -cc file.nz files/*

to compress the files

To unpack, your line should be

./nz x -ofile_copy file.nz 

Note the lack of space between -o and its argument (run nz without arguments to see the syntax). You should also just define a single output directory argument; the * in your -o file_copy/* is expanded by the shell to

• nothing if the file_copy dir does not exist or is empty, and to
• the files currently in the file_copy dir if it is not empty.

On my system, the binary just segfaults though, so I can’t try it “for real”.

by Daniel Andersson from http://superuser.com/questions/415375