Rubyでグローバル変数の一覧を表示するには、global_variablesを使います。
使用例
Railsプロジェクトで実行してみました。
p global_variables
=> [:$trace, :$<, :$., :$FILENAME, :$-i, :$*, :$-p, :$-l, :$-a, :$CGI_ENV, :$ERROR_INFO, :$ERROR_POSITION, :$FS, :$FIELD_SEPARATOR, :$OFS, :$OUTPUT_FIELD_SEPARATOR, :$RS, :$INPUT_RECORD_SEPARATOR, :$ORS, :$OUTPUT_RECORD_SEPARATOR, :$INPUT_LINE_NUMBER, :$NR, :$LAST_READ_LINE, :$DEFAULT_OUTPUT, :$DEFAULT_INPUT, :$PID, :$SAFE, :$CHILD_STATUS, :$LAST_MATCH_INFO, :$PROCESS_ID, :$ARGV, :$MATCH, :$IGNORECASE, :$?, :$$, :$PREMATCH, :$POSTMATCH, :$LAST_PAREN_MATCH, :$~, :$&, :$`, :$', :$+, :$=, :$KCODE, :$-K, :$fileutils_rb_have_lchown, :$verbose, :$fileutils_rb_have_lchmod, :$,, :$/, :$;, :$-F, :$\, :$-0, :$_, :$VERBOSE, :$-v, :$:, :$-I, :$LOAD_PATH, :$", :$LOADED_FEATURES, :$0, :$-w, :$-W, :$DEBUG, :$-d, :$thor_runner, :$PROGRAM_NAME, :$binding, :$_sass_warned_for_unquote, :$arel_silence_type_casting_deprecation, :$@, :$!, :$stdin, :$stdout, :$stderr, :$>, :$_sass_deprecated_interp_warnings, :$1, :$2, :$3, :$4, :$5, :$6, :$7, :$8, :$9]