dvliman

$: (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.
$` (Dollar Backtick) contains the string before the actual matched string of the previous successful pattern match.