Ruby Cheat Sheet

Explore key concepts, syntax, and usage examples for Ruby — perfect for quick reference.

Resource
Online Related
Array
File
String
Math
Integer
Numeric
Object
Hash
Regexp
IO
Methods Namespace
Time
ARGF
BasicObject
Bignum
Class
Complex
Encoding
Methods Namespace
Enumerator
Methods Namespace
Exception
Fiber
Float
Fixnum
Kernel
Method
Module
Proc
Process
Methods Namespace
Random
Range
Rational
Symbol
Thread
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 pattern match in this scope.
  • $`
    💡 The string to the left of the last successful match.
  • $'
    💡 The string to the right of the last successful match.
  • $+
    💡 The last bracket 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.
  • $>
    💡 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 extention, 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.
Global Constant
  • 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 depricated).
  • RUBY_RELEASE_DATE
    💡 The relase date string.
  • RUBY_PLATFORM
    💡 The platform identifier