ruby dollar sign $ global variable

ruby_dollar_signs.txt

$: (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.
$’ (Dollar Apostrophe)     contains the string after the actual matched string of the previous successful pattern match.
$! (Dollar Bang)           contains the Exception that was passed to raise.
$@ (Dollar At Symbol)      contains the backtrace for the last Exception raised.

Alternate Explaination (from diff site)
$!	latest error message
$@	location of error
$_	string last read by gets
$.	line number last read by interpreter
$&	string last matched by regexp
$~	the last regexp match, as an array of subexpressions
$n	the nth subexpression in the last match (same as $~[n])
$=	case-insensitivity flag
$/	input record separator
$\	output record separator
$0	the name of the ruby script file
$*	the command line arguments
$$	interpreter's process ID
$?	exit status of last executed child process

Alternatives using ruby/English https://github.com/ruby/English
$: -> $LOAD_PATH
$" -> $LOADED_FEATURES
$0 -> $PROGRAM_NAME
$! -> $ERROR_INFO
$@ -> $ERROR_POSITION
$; -> $FIELD_SEPARATOR / $FS
$, -> $OUTPUT_FIELD_SEPARATOR / $OFS
$/ -> $INPUT_RECORD_SEPARATOR / $RS
$\ -> $OUTPUT_RECORD_SEPARATOR / $ORS
$. -> $INPUT_LINE_NUMBER / $NR
$_ -> $LAST_READ_LINE
$> -> $DEFAULT_OUTPUT
$< -> $DEFAULT_INPUT
$$ -> $PROCESS_ID / $PID
$? -> $CHILD_STATUS
$~ -> $LAST_MATCH_INFO
$= -> $IGNORECASE
$* -> $ARGV / ARG