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<password> '*.part1.rar'