Special Variables

MRI's Special Variables:

• list of all special variables

  • $! $" $$ $& $' $* $+ $, $/ $; $: $-W $-a $DEBUG $-i $-l $-p $VERBOSE $-v $-w $. $0 $1 $< $= $> $? $@ $FILENAME $SAFE $
    $_$` $stderr $stdin $~

• Grouping by scope / accessibility

scope	access
global	read/write	$" $, $/ $: $DEBUG $-i $VERBOSE $-v $-w $. $0 $> $\ $stderr $stdin
global	read-only	$$ $* $-W $-a $-l $-p $< $FILENAME
thread	read/write	$@ $SAFE
thread	read-only	$! $?
local/thread	read/write	$_
local/thread	read-only	$& $' $+ $1 $` $~
($KCODE and $= are deprecated)

• Grouping by Module

module	variables
(Core)	$! $, $DEBUG $VERBOSE $@ $SAFE $\
IO	$/ $. $> $_ $stderr $stdin
Regexp	$& $' $+ $; $1 $` $~
Process	$$ $0 $?
String	$;
require	$" $:
bin/mruby	$* $-a $-i $-l $-p $-v $-w $0 $< $FILENAME
(Note: $; is in both String and Regexp. $0 is in both Process and bin/mruby)

• aliases:

  • $" = $LOADED_FEATURES
  • $/ = $-O
  • $; = $-F
  • $: = $LOAD_PATH = $-I
  • $DEBUG = $-d
  • $0 = $PROGRAM_NAME
  • $> = $stdout

• Implementation

  • $! : mrb_obj_value(mrb->exc)
  • $$ : return Process.pid
  • $& : $~[0]
  • $' : $~.post_match
  • $* : return ARGV
  • $+ : $~.[-1]
  • $0 : mrb_str_new...(..., ARGV[0] or getprogname())
  • $1 : $~[1]
  • $< : ...?
  • $? : can be a module variable of Process
  • $@ : ...?
  • $_ : set by IO#gets, IO#readline, Kernel.gets and Kernel.readline
  • $` : $~.pre_match
  • $~ : set by Regexp....
  • (same as a global variable) : $" $, $/ $; $: $. $> $stderr $stdin
  • (won't support but implementation should be trivial): $-W $-a $DEBUG $-i $-l $-p $VERBOSE $-v $-w $FILENAME $SAFE $\

Global Variables

• stored in (struct iv_tbl *)mrb->globals

Reference

• Special Variables in MRI 2.1.0 (in Japanese): http://docs.ruby-lang.org/ja/2.1.0/class/Kernel.html#V_--21