Ruby’s predefined variables affect the behavior of the entire program, so their use in libraries is not recommended.
The values in most predefined variables can be accessed by alternative means.
Following table lists all the Ruby’s predefined variables.
| Sr.No. | Variable Name & Description |
|---|---|
| 1 | $!The last exception object raised. The exception object can also be accessed using => in rescue clause. |
| 2 | $@The stack backtrace for the last exception raised. The stack backtrace information can retrieved by Exception#backtrace method of the last exception. |
| 3 | $/The input record separator (newline by default). gets, readline, etc., take their input record separator as optional argument. |
| 4 | $\The output record separator (nil by default). |
| 5 | $,The output separator between the arguments to print and Array#join (nil by default). You can specify separator explicitly to Array#join. |
| 6 | $;The default separator for split (nil by default). You can specify separator explicitly for String#split. |
| 7 | $.The number of the last line read from the current input file. Equivalent to ARGF.lineno. |
| 8 | $<Synonym for ARGF. |
| 9 | $>Synonym for $defout. |
| 10 | $0The name of the current Ruby program being executed. |
| 11 | $$The process pid of the current Ruby program being executed. |
| 12 | $?The exit status of the last process terminated. |
| 13 | $:Synonym for $LOAD_PATH. |
| 14 | $DEBUGTrue if the -d or –debug command-line option is specified. |
| 15 | $defoutThe destination output for print and printf ($stdout by default). |
| 16 | $FThe variable that receives the output from split when -a is specified. This variable is set if the -a command-line option is specified along with the -p or -n option. |
| 17 | $FILENAMEThe name of the file currently being read from ARGF. Equivalent to ARGF.filename. |
| 18 | $LOAD_PATHAn array holding the directories to be searched when loading files with the load and require methods. |
| 19 | $SAFEThe security level0 → No checks are performed on externally supplied (tainted) data. (default)1 → Potentially dangerous operations using tainted data are forbidden.2 → Potentially dangerous operations on processes and files are forbidden.3 → All newly created objects are considered tainted.4 → Modification of global data is forbidden. |
| 20 | $stdinStandard input (STDIN by default). |
| 21 | $stdoutStandard output (STDOUT by default). |
| 22 | $stderrStandard error (STDERR by default). |
| 23 | $VERBOSETrue if the -v, -w, or –verbose command-line option is specified. |
| 24 | $- xThe value of interpreter option -x (x=0, a, d, F, i, K, l, p, v). These options are listed below |
| 25 | $-0The value of interpreter option -x and alias of $/. |
| 26 | $-aThe value of interpreter option -x and true if option -a is set. Read-only. |
| 27 | $-dThe value of interpreter option -x and alias of $DEBUG |
| 28 | $-FThe value of interpreter option -x and alias of $;. |
| 29 | $-iThe value of interpreter option -x and in in-place-edit mode, holds the extension, otherwise nil. Can enable or disable in-place-edit mode. |
| 30 | $-IThe value of interpreter option -x and alias of $:. |
| 31 | $-lThe value of interpreter option -x and true if option -lis set. Read-only. |
| 32 | $-pThe value of interpreter option -x and true if option -pis set. Read-only. |
| 33 | $_The local variable, last string read by gets or readline in the current scope. |
| 34 | $~The local variable, MatchData relating to the last match. Regex#match method returns the last match information. |
| 35 | $ n ($1, $2, $3…)The string matched in the nth group of the last pattern match. Equivalent to m[n], where m is a MatchData object. |
| 36 | $&The string matched in the last pattern match. Equivalent to m[0], where m is a MatchData object. |
| 37 | $`The string preceding the match in the last pattern match. Equivalent to m.pre_match, where m is a MatchData object. |
| 38 | $’The string following the match in the last pattern match. Equivalent to m.post_match, where m is a MatchData object. |
| 39 | $+The string corresponding to the last successfully matched group in the last pattern match. |