jooeycheng

$: (Dollar Colon)          is basically a shorthand version of $LOAD_PATH. 
                           contains an array of paths that your script will search through when using require.
$0 (Dollar Zero)           contains the name of the ruby program being run. This is typically the script name.
$* (Dollar Splat)          is basically shorthand for ARGV. $* contains the command line arguments that were passed to the script.
$? (Dollar Question Mark)  returns the exit status of the last child process to finish.
$$ (Dollar Dollar)         returns the process number of the program currently being ran.
$~ (Dollar Tilde)          contains the MatchData from the previous successful pattern match.
$1, $2, $3, $4 etc         represent the content of the previous successful pattern match.
$& (Dollar Ampersand)      contains the matched string from the previous successful pattern match.
$+ (Dollar Plus)           contains the last match from the previous successful pattern match.