If for some reason you have a directory full of RAR archives, and each is split into parts, extracting them individually can be a pain. If you just type “unrar *” into the terminal, you will extract each file multiple times depending on how many “parts” it has. First, install the “unrar” package:

sudo aptitude install unrar

then cd to the directory with all of your RAR archives. Then type:

unrar e '*.part1.rar'

make sure to keep the single quotes.
If the rar is password protected, add the “-p” switch followed by the password without any spaces.

unrar e -p
 '*.part1.rar'