environment variables in ruby

gistfile1.txt

Pseudo variables

self     the receiver of the current method
nil      the sole instance of the Class NilClass(represents false)
true     the sole instance of the Class TrueClass(typical true value)
false    the sole instance of the Class FalseClass(represents false)
__FILE__ the current source file name.
__LINE__ the current line number in the source file.ù


Pre-defined variables

$!         The exception information message set by 'raise'.
$@         Array of backtrace of the last exception thrown.
$&         The string matched by the last successful match.
$`         The string to the left  of the last successful match.
$'         The string to the right of the last successful match.
$+         The highest group matched by the last successful match.
$1         The Nth group of the last successful match. May be > 1.
$~         The information about the last match in the current scope.
$=         The flag for case insensitive, nil by default.
$/         The input record separator, newline by default.
$\         The output record separator for the print and IO#write. Default is nil.
$,         The output field separator for the print and Array#join.
$;         The default separator for String#split.
$.         The current input line number of the last file that was read.
$<         The virtual concatenation file of the files given on command line (or from $stdin if no files were given).
$>         The default output for print, printf. $stdout by default.
$_         The last input line of string by gets or readline.
$0         Contains the name of the script being executed. May be assignable.
$*         Command line arguments given for the script sans args.
$$         The process number of the Ruby running this script.
$?         The status of the last executed child process.
$:         Load path for scripts and binary modules by load or require.
$"         The array contains the module names loaded by require.
$DEBUG     The status of the -d switch.
$FILENAME  Current input file from $<. Same as $<.filename.
$LOAD_PATH The alias to the $:.
$stderr    The current standard error output.
$stdin     The current standard input.
$stdout    The current standard output.
$VERBOSE   The verbose flag, which is set by the -v switch.
$-0        The alias to $/.
$-a        True if option -a is set. Read-only variable.
$-d        The alias to $DEBUG.
$-F        The alias to $;.
$-i        In in-place-edit mode, this variable holds the extension, otherwise nil.
$-I        The alias to $:.
$-l        True if option -l is set. Read-only variable.
$-p        True if option -p is set. Read-only variable.
$-v        The alias to $VERBOSE.
$-w        True if option -w is set.


Pre-defined global constants

TRUE              The typical true value.
FALSE             The false itself.
NIL               The nil itself.
STDIN             The standard input. The default value for $stdin.
STDOUT            The standard output. The default value for $stdout.
STDERR            The standard error output. The default value for $stderr.
ENV               The hash contains current environment variables.
ARGF              The alias to the $<.
ARGV              The alias to the $*.
DATA              The file object of the script, pointing just after __END__.
RUBY_VERSION      The ruby version string (VERSION was deprecated).
RUBY_RELEASE_DATE The release date string.
RUBY_PLATFORM     The platform identifier.