Reference Guide
Ruby Reference Guide
There are many Ruby references guides, but this one is mine.
Keywords
__ENCODING__ # The script encoding of the current file
__END__ # Marks the end of the Ruby program; DATA can follow
__FILE__ # The path to the current file
__LINE__ # The line number of this keyword in the current file
BEGIN # Runs before any other code in the current file
END # Runs after any other code in the current file
DATA # An IO stream to read data embedded in the program following __END__
def # Defines a method
defined? # Returns a string describing its argument
do # Starts a block
alias # Creates an alias between two methods (and other things)
and # Short-circuit Boolean and with lower precedence than &&
begin # Starts an exception handling block
break # Leaves a block early
case # Starts a case expression
class # Creates or opens a class
def # Defines a method
defined? # Returns a string describing its argument
do # Starts a block
else # The unhandled condition in case, if and unless expressions
elsif # An alternate condition for an if expression
end # The end of a syntax block.
ensure # Starts a section of code that is always run when an exception is raised
false # Boolean false
for # A loop that is similar to using the each method
if # Used for if and modifier if expressions
in # Used to separate the iterable object and iterator variable in a for loop
module # Creates or opens a module
next # Skips the rest of the block
nil # A false value usually indicating “no value” or “unknown”
not # Inverts the following boolean expression. Has a lower precedence than !
or # Boolean or with lower precedence than ||
redo # Restarts execution in the current block
rescue # Starts an exception section of code in a begin block
retry # Retries an exception block
return # Exits a method
self # The object the current method is attached to
send # Invoke a method
__send__ # Alternative for the above, in case of name clashes
super # Calls the current method in a superclass
then # Indicates the end of conditional blocks in control structures
true # Boolean true
undef # Prevents a class or module from responding to a method call
unless # Used for unless and modifier unless expressions
until # Creates a loop that executes until the condition is true
when # A condition in a case expression
while # Creates a loop that executes while the condition is true
yield # Starts execution of the block sent to the current methodComments
#This is a single line comment
=begin
This is a multiline comment
This is a multiline comment
=endVariables
_age = 21 # local variable
1age = 21 # INVALID variable name
age = 21 # local variable
@age = 21 # instance variable
@@age = 21 # class variable
$age = 21 # global variableConstants
AGE = 21 # constant; by convention - constants can be modified and generate a warningInteger Numbers
1234 # Fixnum decimal
-1234 # Negative Fixnum
1_234 # Fixnum decimal (with underscore to improve readability)
0b1011 # binary
0xff # hexadecimal
0377 # octal
12345678901234567890 # BignumFloating Numbers
123.4 # floating point value
4.0e2 # 400.0 - scientific notation
4E2 # 400.0 - dot not required
4e+2 # 400.0 - sign before exponentialBackslash notations
(also ''escaped characters')
\n # Newline (0x0a)
\r # Carriage return (0x0d)
\f # Formfeed (0x0c)
\b # Backspace (0x08)
\a # Bell (0x07)
\e # Escape (0x1b)
\s # Space (0x20)
\x # Character x``
\nnn # Octal (n = 0-7)
\xnn # Hesadecimal (n = 0-9, a-f, A-F)
\cx, \C-x # Control-x
\M-x # Meta x; usually used for keyboard/terminal control
\M-\C-x # Meta-Control-x; usually used for keyboard/terminal control
\unnnn # Unicode code point U+nnnn (Ruby 1.9+)
puts "ln1\nln2" # Newline (0x0a); prints two lines
puts "n123\rab" # Carriage return (0x0d); prints one line, "ab23"
puts "f12\f345" # Formfeed (0x0c); prints two lines, offset
puts "abc\bx" # Backspace (0x08); prints 'abx'
puts "bell\a\a\a" # Bell (0x07); prints 'bell' and rings bell three times
puts "ab\ecd" # Escape (0x1b); prints 'abd'
puts "ab\scd" # Space (0x20); prints 'ab cd'
puts "ab\xcd" # Character x; prints 'abxcd'
puts "ab\015x" # Octal (n = 0-7); prints 'xb', same as \r
puts "ab\xdx" # Hesadecimal (n = 0-9, a-f, A-F); prints 'xb', same as \r
puts "abc\C-Hxyz" # Control-x; prints 'abxyz', same as \b; \C-@ == \x00, \C-A == \x01, ...
puts "\u2713" # Unicode code point U+nnnn (Ruby 1.9+); prints "✓"Percent Literals
# can use any paired delimiters
# Uppercase versions (as in %I, %Q) allow interpolation and escaped characters
baz = "abc"
%I{foo bar #{baz}} # Array of Symbols: [:foo, :bar, :abc]
%i{foo bar #{baz}} # Array of Symbols: [:foo, :bar, :"\#{baz}"]
%q(use a " here) # Strings: "use a " here"
%{...} # Alternative Strings notation
%r{/home/user} # RegExp: \/home\/user
%s{fancy symbol} # Symbol: :"fancy symbol" (not recommended)
%w{foo bar baz} # Array of Strings: ["foo", "bar", "baz"]
%x{cat __FILE__} # Backtick: the contents of the current fileHERE Docs
str1 = <<EODOC
This is some data to
go into
the str1 variable
EODOC
puts str1 # Exact text, with carriage returns, in str1
str2 = <<-INDENTED
More dumnmy text, indented.
Leading spaces are included in the output
#{str1} - yes, interpolation is supported
INDENTED
puts str2 # Exact text including indent spaces; HERE marker can be indented
str3 = <<"***"
You can use special characters,
enclosed in quqotes.
***
puts str3 # Exact text
str4 = <<~SQUIGGLY_DOC
The tilde '~" modifies the indentation
of the text. The leading spaces of the
least-indented line are removed from all lines.
This line will be indented two spaces.
SQUIGGLY_DOC
puts str4 # Modified indentation, as noted in the text
str5 = <<'NO_INTERPOLATION'
Enclosing the HEREDOC identifier in
sinqle quotes means no interpolation,
so #{str4} is printed character-for-character.
puts str5 # HEREDOC with no interpolation
str6 <<`BACKTICKS`
cat #{__FILE__}
BACKTICKS
puts str6 # Prints the results of the cat commandArrays
array = [] # Array; zero-based indexing
array = Array.new(5) # Array with size
array = Array.new(2, "abc") # ["abc", "abc"]
array = Array(0..9) # [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
first_item = array.first # Array first item
first_item = array[0] # Array first item
last_item = array.last # Array last item
last_item = array[array.size - 1] # Array last_item
array.size # Array size
array.length # Array size
array.count # Array size
array.at(5) # Element at index 5
array.push(42) # Add 42 to end of array
array.pop # Remove last element from array
array.shift # Remove first element from array
array.unshift(15) # Add 15 to beginning of array
array.include?("abc") # Return true if the value is present in array
array.take(2) # Return the first n itens of the array
array.drop(2) # Drops first n elements from array and returns the rest of the elements as a new array
array.index("abc") # Return index of "abc" in array or nil if not found
array.sort # Return a new sorted array
array.sort! # Perform a sort operation in array directly
array.delete("abc") # Delete all items in array that are equals to obj "abc" given as parameter. Return last item deleted or nil if item was not found
array.insert(1, "xyz") # Inserts the given values before the element with the given index. Needed to pass index and objects as parameters
array.empty? # Return true if the array has no elements
array.uniq # Return a new array removing duplicated values
array.uniq! # Remove duplicated values from array
array.methods.sort - Object.methods # List all Array instance methods
array = %w{a b c #{num}} # ["a", "b", "c", "\#{num}"]
array = %W{a b c #{num}} # ["a", "b", "c", "5"] (if num = 5)Hash
hash = {} # New Hash without default value
hash = Hash.new("default_value") # New hash with a default value for any key
hash.default = "another_value" # Changes default value
hash.size # Hash size
hash.length # Hash size
hash.count # Hash size
hash[1] # Get the value or default if key not found
hash.clear # Removes all key-value pairs from hash
hash.delete(1) # Deletes a key-value pair by key
hash.empty? # Test if hash is empty (true or false)
hash.invert # New hash with inverted key-value pairs
hash.values # Returns a new array containing all the values of hash.Class
class Customer
endOperators
# Arithmetic Operators
a + b # Adition
a - b # Subtraction
a * b # Multiplication
a / b # Division
a % b # Modulus
a**b # Exponent
# Comparison Operators
a == b # Checks if the value of two operands are equal
a != b # Checks if the value of two operands are different
a > b # Checks if the value of left operand is greater than the value of right operand
a < b # Checks if the value of left operand is less than the value of right operand
a >= b # Checks if the value of left operand is greater than or equal to the value of right operand
a <= b # Checks if the value of left operand is less than or equal to the value of right operand
a <==> b # Returns 0 if first operand equals second, 1 if greater and -1 if less
(1...10) === 5 # Used to test equality within a when clause of a case statement
a.eql?(b) # Check if the type and value are equals
a.equal?b # Check if the the objects have the same id
# Logical Operators
a && b # "and" operator (higher precedence)
a and b # "and" operator
a || b # "or" operator (higher precedence)
a or b # "or" operator
!a # Negation operator (higher precedence)
not a # Negation operator
# Bitwise Operators
a = 60 # 0011 1100 in binary format
b = 13 # 0000 1101 in binary format
------------------
a&b # 0000 1100
a|b # 0011 1101
a^b # 0011 0001
~a # 1100 0011
# Parallel Assignment
a, b, c = 10, 20, 30 # a = 10, b = 20, c = 30
a, b = b, c # Swapping the values
# Ternary Operator
true ? "true" : "false" # Result is "true"Ranges
(1..10) # Creates a range from 1 to 10 inclusive
(1...10) # Creates a range from 1 to 9
('a'..'d') # 'a', 'b', 'c', 'd'
(1..10).to_a # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
('bar'..'bat').to_a # ["bar", "bas", "bat"]
# Range methods
range1 = (1..10) # Creates a range from 1 to 10 inclusive
range1.include?(5) # Return true
range1.min # Return the min value
range1.max # Return the max value
range1.reject {|i| i < 5 } # Return [5, 6, 7, 8, 9, 10]Strings
'Simple string literal' # Simple string literal
myString = String.new("TEST") # Create an instance of String object
foo = myString.downcase # Return a downcased copy of the string
foo = myString.downcase! # Downcase the content of string with self-assignment
foo = myString.upcase # Return a upcased copy of the string
foo = myString.upcase! # Upcase the content of string with self-assignment
foo = myString.capitalize # First character converted to uppercase
foo = myString.capitalize! # First character converted to uppercase with self-assignment.
foo = myString.count "T" # Return the number of "T" character inside myString
foo = myString.empty? # Return true if the string has length equals 0
foo = myString.size # Return the number of character length
foo = myString.reverse # Return a new string with the characters in reverse order
foo = myString.reverse! # Reverse the content of string with self-assignment
foo = myString.delete "S" # Return a copy of all characters in intersection of its arguments deleted
foo = myString.delete! "S" # Perform a delete operation in string with self-assignment. Returning nil if the string was not modified.
foo = myString.split '' # Divides str into substrings based on a delimiter, returning an array of these substrings.
#String concatenation
myString << "S" # concat string "S" directly into myString
foo = myString + "S" # Return a new string with concatenation of myString and "S" character
#String interpolation
"Do the unit #{foo}" # Return a new string concatenated with foo variable.Conditional Structures
# simple if statement - most commmon structure for decisions
if expression
# some code that will only be executed if expression is true.
end
# an alternative for a if statement is using the ternary expression
# though these are not so easy to read, they can be helpful.
missed_class ? 'the alumn missed class' : 'the alumn was present'
# the expression above returns the first string if missed_class is true, otherwise
# it returns the second string.
# if/else statement
if expression
# some code that will only be executed if expression is true.
else
# block of code that will only be executed if expression is false.
end
# elsif statement
if expression_1
# some code that will only be executed if condition_1 is true.
elsif expression_2
# some code that will only be executed if condition_1 is false and
# condition_2 is true.
else
# some code that will only be executed if both conditions are false.
end
# expressions may or may not be encapsulated into parenthesis.
if (expression)
# some code that will only be executed if condition is true.
else
# some code that will only be executed if condition is false.
end
# unless statement - an modified if statement to use when the expression is
# expected to be false
unless expression
# some code to be executed if the expression is FALSE
else
# some code to be executed if the expression is true
end
# case/when structure
case
when a < 1
# code that will be executed if 'a' value is smaller than 1.
when a == 1
# code that will be executed if 'a' value matches 1.
when a > 1
# code that will be executed if 'a' value is greater than 1.
end
# breaking conditional expressions
if condition_or_expression; some_code; end
if condition_or_expression then some_code; end
if condition_or_expression; some_code; else; more_code; end
# addressing variable values conditionaly
# using if statements:
child.name = if (child.gender == 'female')
'Jane Doe'
else
'John Doe'
end
# or
child.name = if (child.gender == 'female'); 'Jane Doe'; else; 'John Doe' end
# or even
child.name = child.gender == 'female' ? 'Jane Doe' : 'John Doe'
# using case statement:
variable_status = case
when a < 1
'the number is smaller than 1'
when a == 1
'the number equals 1'
when a > 1
'the number is grater than 1'
endLoops
# For Statement - Executes code once for each element in expression
for i in 1..10
puts i # Prints 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
end
# While Statement - Executes code while the condition is true
count = 0
while count < 5
puts count # Prints 0, 1, 2, 3, 4
count += 1
end
# Until Statement - Executes code while the condition is false
count = 5
until count == 0
puts count # Prints 5, 4, 3, 2, 1
count -= 1
end
# Loop - Loops until you manually press Ctrl+C or insert a break statement inside the block
count = 0
loop do
puts count # Prints 0, 1, 2
count += 1
break if count == 3
end
# Each Iterator - Loops through each element inside the collection
(1..5).each do |i|
puts i # Prints 1, 2, 3, 4, 5
end
# Break Statement - Leaves a block early
for i in 1..10
if i == 5
break
end
puts i # Prints 1, 2, 3, 4
end
# Redo Statement - Restarts the current iteration of the most internal loop, without checking loop condition
for i in 0..5
puts i # Prints 0, 1, 2, 3, 3, 3, ... (infinite loop)
redo if i > 2
end
# Next Statement -Jumps to the next iteration of the most internal loop
for i in 1..5
if i == 3
next
end
puts i # Prints 1, 2, 4, 5
endI/O
puts variable_name # Displays the value stored in the variable and jumps to next line
variable_name = gets # Takes any input from the user from standard input called STDIN
putc variable_name # Displays just one character
print variable_name # Displays the value stored in the variable (no line break)Methods
# Simple Method
def method_name
end
# Method with parameters
def method_name (var1, var2)
end
# Method with parameters (with default values)
def method_name (var1 = value1, var2 = value2)
endBlocks
# The block is passed a counter as a parameter.
# Calling the "each" method with a block looks like this:
(1..5).each do |counter|
puts "iteration #{counter}"
end
# Output:
#=> iteration 1
#=> iteration 2
#=> iteration 3
#=> iteration 4
#=> iteration 5
# You can also surround blocks in curly brackets:
(1..5).each { |counter| puts "iteration #{counter}"}
# Here’s a basic example of a multi-line block
[1, 2, 3].each do |n|
# Prints out a number
puts "Number #{n}"
end
# Here’s a basic example of a inline block
[1, 2, 3].each { |n| puts "Number #{n}" }
# Ruby program to demonstrate how block returns the values
# here two methods called 'select' and 'even?'
# even? method is called inside the block
puts [1, 2, 3, 4, 5].select { |num| num.even? }
# Output:
#=> iteration 12
#=> iteration 14
# here india_states is an array and
# it is the argument which is to
# be passed to block
california_cities = ["San Diego", "Pasadena",
"Venice Beach", "Rancho Cucamonga",
"Ontario" ]
# passing argument to block
california_cities.each do |california_cities|
puts california_cities
end
# Output:
#=> San Diego
#=> Pasadena
#=> Venice Beach
#=> Rancho Cucamonga
#=> Ontario
# Ruby program to demonstrate the 'yield' statement
# Parameters can be passed to the yield statment.
# method
def method_name
# statement of the method to be executed
puts "Inside Method!"
# using yield statement
yield
# statement of the method to be executed
puts "Again Inside Method!"
# using yield statement
yield
end
# block
method_name{puts "Inside Block!"}
# Output:
#=> Inside Method!
#=> Inside Block!
#=> Again Inside Method!
#=> Inside Block!
# Ruby program to demonstrate the use of
# same variable outside and inside a block
# variable 'x' outside the block
x = "Outside the block"
# here x is inside the block
4.times do |x|
puts "Value Inside the block: #{x}"
end
puts "Value Outside the block: #{x}"
# Outputs:
#=> Value Inside the block: 0
#=> Value Inside the block: 1
#=> Value Inside the block: 2
#=> Value Inside the block: 3
#=> Value Outside the block: Outside the blockLast updated