Here's how to do it with the unrar program provided by the unrar package under Ubuntu, which identifies itself like this when the --help option is passed:
UNRAR 3.70 beta 3 freeware Copyright (c) 1993-2007 Alexander Roshal
If the files are found in the path /home/me/rarfiles, and you want to unrar them into /home/me/unrarfiles:
for f in /home/me/rarfiles/*.rar; do
unrar -o+ x "$f"
The -o+ means to overwrite any files which already exist, so if some rar files contain files with similar names, you will end up with only the last one from the last rar file which contained that file name. Omit this and you will be prompted if there are duplicates if you want to overwrite.