find . -name "*.rar" -exec unrar x '{}' \;
Let me explain what this does.
"find ." - will find files within the current directory and any subdirectories
"-name "*.rar" - will only find *.rar files
"-exec " - will perform an external command on the results found by the "find" command.
"unrar x" - is the command to extract the rar archives
"'{}'" - tells find to append the found result to the end of the exec'd command.
"\;" - signifies the end of the exec'd command.
forrás