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This file contains 2 sections:
1: Chapter & Headings
2: Sample Content

Chapter& Headings
Introduction To Ruby
* What is Ruby
* Origin of Ruby
* Version History
* Language Features
* Supported Operating Systems
* Installation Options
* Using irb (as a REPL tool)
* Running ruby tools (ruby -v, ri,rdoc)
* Create a Hello World
* Shebang (on Unix)
* ftype on Windows
IDEs
* Editing Ruby in a text editor
* Benefits of IDEs
* List of IDEs
* Using Eclipse
* Create Hello World in Eclipse
Language Fundamentals
* Script Structure
* Function
* Blocks
* Reserved Words
* Syntax Rules
* Naming Identifiers
* Comments
Datatypes
* What is a Datatype
* List of Datatypes
* Literals
* Numbers
* String
* Boolean

* Time
* Nil
* Constants
* Creating
* Predefined __FILE__, __LINE__, ARGV, DTA
* Variables
* Local
* Instance
* Class
* Global
* Pseudo
String Closer Look
* Single quotes
* %q
* Double quotes
* %Q
* Escape Sequences
* Assignment (reference vs value)
* Interpolation
* Here documents
* String methods
Collections
* What are collection types
* Array intro
* Hash intro
* Arrays
* Creating Arrays
* Adding values to Arrays
* Ranges
* Useful Array Methods
* Hash
* Creating Hash
* Subscripting with Symbols
* Useful Hash Methods
Operators
* Arithmetic

* Relational
* Logical
* Concatenation
* Assignment
* Shorthand
* Multiple Assignment
* Parrallel Assignment
* Conditional Assignment
Branching Statements
* What is branching
* if
* unless
* if-else
* if-elsif-else
* short-if
* case
Loops
* while
* until
* for
* Loop modifiers
* break
* next
* redo
* Iterators
* Introduction
* do/end
* { }
* Numerical Iterators
* String Iterators
* Collection Iterators

What Is Ruby
 Ruby is a server-side, object-oriented scripting-language.
 Ruby development was started in 1993 by Yukihiro “Matz”
Matsumoto.
 Ruby was developed as an alternative language to Perl and Python
and borrows from both languages.
 Many operations support both the Perl & Python constructs.
E.g. both || (Perl) and or (Python) are supported.
 Ruby runs on Linux, Mac and Windows operating systems.
 It is pre-installed on Macs and certain versions of Linux.
 Like other languages, Ruby has undergone various revisions.
 Version 1.9.0 was released in December 2007.
 Version 2.0.0 was released in February of 2013.
 Version 2.2.0 was released in December of 2015.

Language Features
 Ruby is a fully objectoriented language. Everything is an object
instance including literals.
 Every object has a type. This type is the class the object is based
on.
 Every object has methods
 Ruby is flexible and allows you to create the following types of
code:
 Classes: These are structures that hold data and methods
 Modules: These are groupings of methods.
 Scripts: Ruby also allows you to write executable script outside
of both classes and modules.
 Ruby is dynamically typed.
 Ruby is interpreted. Which means the code must be available at
execution time.

Supported Operating Systems
 Ruby is supported by all major operating systems i.e Linux,
Mac OS X, Windows.
 Ruby comes pre-installed on Mac OS X and many distributions
of Linux.
 Ruby is available on Windows too and is fully supported there.
 Ruby runs slower on Windows, since the ‘require’
statement in Ruby scripts take a good chunk of time on
Windows platform.
 Ruby (v 1.9.2 ) has passed all the core tests on Windows.

Installation Options
 In Mac OS X, Ruby can be installed with the following options:
 RVM
 Homebrew
 Fink
 MacPorts
 In Linux systems, each variant has its own way to install Ruby.
 Debian/Ubuntu systems use Synaptic or apt.
 Red Hat Linux uses command line tool RPM
 Ruby can be installed on Windows in following ways:
 Downloading compiled binaries from Ruby site
 RubyInstaller
 Cygwin

Using IRB
 Ruby comes in interactive mode too which can be put into use
by using Interactive Ruby Shell( irb).
 IRB acts as a read-eval-print loop tool for Ruby where actual
Ruby code can be executed.
 IRB can be used by typing irb in a UNIX-basedshell prompt.
 IRB output is slightly different than the actual Ruby output in
the following way:
 An assignment in IRB also prints out that assigned value
while in actual Ruby code, the value is not printed just
assigned.

Running Ruby Tools
 There are several handy tools that can be used along with Ruby
 ruby –v
 RDoc
 Ri
 RDoc is a Ruby gems that automatically creates documentation
from the comments and structure of your Ruby code.
 Ri provides offline help for Ruby and acts as a command line
manual for Ruby language.
 ri Enumerator will open docs for Enumerator class.

Create a Hello World
 In Unix systems create a hello_world.rb file and include a
shebang line on top of the script. Shebang is ignored by
interpreter as it is treated as a comment.
 Shebang line cannot be preceded by blank lines or any
leading spaces.
 It is used by shell to determine which program to use to
run the script
 In Windows command prompt, use ftype command to point to
the ruby.exe installation path.

Editing Ruby in Text Editor
 Ruby code can be written in any text editor. Some of the popular
text editors to write Ruby code are:
 TextMate is a Mac OS X text editor.
 Sublime Textis available on Linux, Mac OS X and
Windows.
 Vim is available on Linux systems.
 Emacs is a popular Vim alternative.

Benefits of IDE’s
 Code completion and code insight
 Resource Management
 Debugging tools
 Less time to build project.
 Easier Project Management

List of IDE’s
 IDE is one of the most important part tools in a developer’s kit.
The most popular IDE’s for Ruby are following:
 IntelliJ’s RubyMine
 Aptana
 RedCar
 NetBeans
 Eclipse

Using Eclipse
 Eclipse provides support for Ruby with Ruby
Development Tools (RDT) plug-in.
 Allows navigation of Ruby files within a Ruby project.

Hello World with Eclipse
 Create a file with a .rb extension in eclipse after downloading
RDT plugin.
 Use the puts statement to print out “Hello World” in the console.

Script Structure
 Blocks and functions are one of the many important parts of a
Ruby script.
 Keeping with Ruby’s object-oriented design, the functions are
called methods in Ruby.
 Defined with the def keyword
 Return keyword can be used to explicitly return a value.
 Value of the last line executed is returned if return not
used.
 Accepts default value for arguments as well as variable
length arguments.
 Any code surrounded by {…} are blocks in Ruby. But blocks are
more powerful than just that.
 They are also everything inside do…end part in Ruby
code.
 They are also used to construct Proc objects.
 They can be passed to methods as arguments. One per
method.
 Yield keyword used inside methods to evaluate a block.

Reserved Words
 Ruby has some reserved words which can’t be used as
identifiers.
 Some of the reserved words in Ruby v2.1.0 are :
 BEGIN
 END
 case
 self
 yield
 super

Naming Identifiers
 Identifier’s name can be made up of alphanumeric characters
and underscores but cannot start with a digit.
 Identifier’s name length is only limited by a computer’s memory,
otherwise no restrictions.
 Identifiers which are method names can end with a question
mark, equals sign or exclamation mark.
 Reserved words cannot be used as identifiers.

Comments
 Single line comments start with a # character to the end of the
line.
 Tocomment several lines of code, you can use the # symbolat
the start of each line. But this will be inconvenient. A better
approach is to use the Ruby multiline comment feature.
 This is done by using the =begin and =end tags at the start
of the lines you wish to comment.
 Every statement between these tags is considered a
comment.

What is Datatype
 Datatypes are the types of “things” that are used to represent
data in a programming language.
 Literals are the values we assign to a variable.
 Ruby supports various data types:
 Boolean
 Number
 String
 Array
 Hash
 Literals include:
 Booleans and nil
 Symbols
 Regular expressions
 Procs
 Ranges
 Arrays

Numbers
 Numbers consist of two main data types. Integer and Floats.
 Integers are number with no decimal place. They are objects in
Ruby.
 10/3 will yield 3 instead of 3.333 since both of the numbers
are integers.
 Since they are objects, they have methods defined onto
them e.g. 3.times {block}
 Floats are numbers with decimal places.
 10.0/3 will yield 3.333 since one of the numbers is a float.

Strings
 Since everything is an object in Ruby, strings are also objects
belonging to the class String.
 Simplest string literals are enclosed by single quotes.
 String literals can also contain Ruby variables through
expression substitution.
 Strings can also be concatenated in Ruby through multiple ways.
The plus operator (+) is one of the methods.
 Every time a string literal is used for assignment, a new String
object is formed.
 A lot of methods are defined on String objects:
 upcase
 downcase
 length
 One can even open the String class at runtime and define their
own methods for the String class.

Boolean
 Booleans in ruby, just like any other programming language can
just take one of these two values:
 true
 false
 They are used to branch out our code according to conditionals.
 Booleans in ruby are different from truthy and falsey values.

Time
 Time class represents dates and times in Ruby. Storing dates and
time in string literals is bad and not recommended at all.
 There are minor differences between Time and DateTime in
Ruby.
 DateTime has minor understanding of time zones and no
concept of daylight time savings.
 DateTime has no concept of leap seconds.

Nil
 Nil is an object in Ruby too.
 nil.class actually returns NilClass.
 5.nil? and nil.nil? are valid Ruby statements.
 Object_id of nil equals 4 as nil is a singleton instance of NilClass.

Constants
 Constants start with capital letters. “Foo” is a constant while
“foo” isn’t.
 Ruby allows you to redefine and modify the value of constants
but gives a warning during redefining.
 Constants can be frozen by using method “freeze” on constants
which will not allow modification of constants.
 Ruby has some predefined constants too:
 _File_
 _Line_
 ARGV
 DTA

Variables
 Local variables name begins with a lowercase letter or
underscore.
 Accessible from within the blocks of its initialization.
 Scope ends when the function returns.
 Instance variables name begin with @ symbol.
 They belong to an instance. Each instance has its own
copy.
 Uninitialized instance variables are nil by default.
 They are not passed along the inheritance chain.
 Class variables belong to the class unlike instance variables
 They are denoted by @@ syntax.
 Class variables shared by all descendents of the class.
 Act like global variable visible just in the inheritance tree.
 Global variables start with a $ symbol. They can be accessed
anywhere in the program during runtime.
 Pseudo variables are predefined and we cannot assign values to
them. Some of these are :
 self
 nil
 true

Single Quotes
 Single quoted strings cannot be interpolated.
 Single quoted strings can’t be used for expression substitution.
 Single quoted strings are not subject to escape sequences except
for escaping single quotes themselves.
 %q is shorthand syntax to generate single quoted string literals.

Double Quotes
 Double quoted strings can be interpolated.
 Expression substitution can be performed with double quoted
string literals.
 They are subject to escaping sequences.
 %Q is shorthand syntax for double quoted strings.

Escaping sequences
 Some of the escape sequences used inside double quoted string
literals are:
 ” – double quote
 - single backlash
 b – backspace
 n – newline
 s – space
 t – tab

Assignment (Reference vs value)
 String assignment (a = “hello”) always creates new object_ids.
 String assignment (b = a) always stores reference of string
variable.
 Assigning new value to either “a”or “b” won’t affect each other’s
values.
 Usage of methods like gsub! on one string will affect the value of
other one since it will change the value present at the reference.

Interpolation
 Interpolation allows Ruby code to appear within a string.
 Expression can be any valid Ruby code.
 Interpolation requires double-quoted string literals.
 Automatically calls to_s on the result.

Here document
 Here document is constructed by << symbolfollowed by the
identifier marking end of the document.
 End mark is called terminator.
 Here documents are interpolated unless single quotes are used
around the delimiter.
 Multiple here documents can be used together too.

String methods
 Strings have a lot of methods defined onto them.
 Some of the methods are :
 capitalize returns the string with first character in upper
case.
 upcase returns the string with lowercase letters replaced
with their uppercase counterparts.
 downcase returns the string with uppercase letters
replaced with their lowercase counterparts.
 split divides string into substrings based on delimiter and
returns an array.
 hash sums up the characters in a string.
 sum returns a n-bit checksum of the characters in string.

What are collection types
 Collections types are the data types which can hold more than
one item.
 The most used collection types in Ruby are:
 Arrays
 Hashes
 Arrays hold items against an index with random access.
 Hashes hold items in key/value pairs.

Arrays
 Arrays can hold different data types in Ruby. A single array can
consist of strings, integers and even booleans.
 Arrays are indexed by a non-negative integer when accessed
from start.
 Negative integer index accesses the array from the last.

Creating Arrays
 Arrays can be created in two ways:
 array = []
 Array.new
 %w
 String splitting
 In all of the cases, a new array object is constructed in memory
possessing an object_id.
 %w delimiter is used to convert single or double quoted string
literals into arrays.
 Splitting a string with a delimiter converts strings into arrays.

Adding values to arrays
 There is more than one way to add a value in an array object.
 << syntax
 push method
 unshift
 insert
 << and push adds elements to the end of array.
 Unshift method adds elements to the start of the array
 Insert method can be used to add element at any index.

Ranges
 Arrays can be accessed through range of indexes too e.g a[1..3]
 Range has a start point and an end point separated by double
periods or triple periods.
 The end position is counted with double periods but omitted
with tripe periods.

Useful Array Methods
 Array objects have a lot of handful method defined unto
them.
 each iterates over a collection with an iterator
variable holding enumerable value one by one.
 each_with_index iterates over a collection with two
iterator variables representing the enumerable and
the index of the enumerable respectively.
 map is same as each except it returns the modified
enumerable unlike each which returns the original
object.
 collect is same as map. More like an alias fofor map.
 sample chooses a random element(s) from an array.
 permutation yields all permutations for n element of
an array.
 flatten extracts all the elements of an array which
itself are an array into a new array.

Hash
 Hash is a way to store a collection of data in key/value
pairs.
 A key can only appear once in a hash.
 The keys can be strings, symbols or even integers. Mostly,
strings and symbols are preferred.

Creating Hash
 Hashes can be constructed in two ways:
 Explicitly declaring the hash with curly braces {}
 Hash.new
 The value of hash when not initialized is {}.
 The default value of a hash can be specified when by passing a
parameter to Hash.new(“greeting”). This sets the default value
to “greeting”.

Subscripting with symbols
 Ruby symbol is an internal representation of the name.
 Ruby symbols have the same object_id throughout the
application unlike strings which represent different objects with
same literals.
 They are only initialized once.
 They don’t store values or objects.
 After Ruby 2.2.0, symbols can now be garbage collected too.
 Symbol.all_symbols results in all the symbols predefined in
Ruby other than the ones we create.

Useful Hash Methods
 Hashes are equipped with some very handy methods:
 mergecombines one hash with other.
 each iterates over a hash providing a key and value against
it as iterator variables.
 has_keys?checks if a hash contains key(s).
 map

Arithmetic Operators
 Ruby has all the basic arithmetic operators
 + Adds the values on both sides of it.
 - Substracts the value on the right of the operator from the
one of the left.
 * Multiplies the operands.
 / Divides the number on left by the number on right of it.
 % - Modulus operator. Gives the remainder of a division
operation.
 ** - Exponent operator. 2**3 i.e 8

Relational Operators
 Relational operators are constructs that define relationship
between two entities.
 == checks the equality of left and right side variables.
 !== checks if the left and right side are not equal.
 > checks if the left side is greater than the right side.
 < checks if the left side is smaller than the right side.
 >= checks if the left side is greater than or equal to right
side.
 <= checks if the left side is smaller than or equal to the right
side.
 <=> is called the spaceship operator. It returns 0, -1, 1 after
comparing the left value to the right value. If equal, it
returns 0. If left is greater then right, it returns 1. If left
smaller then right, it returns -1. It returns nil otherwise.
 === checks for equality of value and type of the operands.

Logical Operators
 Logical operators are more commonly called Boolean operators.
 and, or, not are logical operators and each of them come in two
versions
 and, &&
 or and ||
 not and !
 The latter versions of each of them have higher precedence than
their former part.

Assignment Operators
 Operators used to assign new value to a variable.
 = (a = 5 assigns a value to a variable)
 += (a+=3 equals a = a+3)
 -= (a-= 3 equals a = a-3)
 *= (a*=3 equals a = a*3)
 /= (a/=3 equals a = a/3)
 %= (a%=3 equals a = a%3)
 **= (a**=3 equals a = a**3)
 ||= (a||=b will assign a to b only if a is undefined or nil)
 Ruby lets you assign multiple variables at once. Supports
multiple assignment e.g a,b = 3,4.
 Parallel assignment works by comparing the left hand side, also
called the receiving side, to the right-hand side.

What is Branching
 Conditional branching takes the result of an expression and
further executes code based on whether the result of expression
is true or false.
 There are many control structures that provide such branching
 if
 else-if
 unless
 while
 case

If expression
 If expressions execute code based on the Boolean value provided
to if condition.
 If expression is terminated by the end statement.
 If expression is one of the most basic element and control
structure often used for branching inside a script.
 If expression can be written in one line if followed by a then
keyword.
 If expression is evaluated on basis of a true-or-false values.
 In Ruby’s context, true and false is a boolean, but there are some
other truthy and falsey values that can be used to evaluate an if
expression.
 Only nil and false will evaluate to false in an if expression in
Ruby.

If-else statement
 The else case of the if-else statement executes when if clause
evaluates to false.
 So the else case will only be considered when if case evaluates to
false.

If-elsif-else expression
 The elsif and else blocks give you further control over your code
since it accommodates further tests.
 There is no limit on the number of elsif blocks but the if and else
block can only be one.

Short-if expression
 Short-if statement is a space-saving short way of evaluating an
expression and returning a value.
 The syntax is :
 (condition)? (expression if true) : (expression if false)
 Also referred to as ternary operator.
 Shortened if statements can also be written as:
 puts “hello” if a == 0

Case expression
 Case is an alternative to the aforementioned if-elsif-else
expression.
 You give an expression to a case keyword and evaluate the
choices in the when keyword.
 The statement when can be supplied with more than
one value.
 When can also be evaluated against string
computation and regular expressions.
 The else keyword can be used as a default value
provider for the case expression in the end.

While loop
 It starts with the while keyword and ends with end keyword.
 The code block in between will keep on executing as long
as the expression provided to while statement evaluates to
true.
 The while loop can shortened too.
 <code> while <expression>

Until loop
 Until statement has the exact same syntax as the aforementioned
while loop.
 Until and while loops are same in functionality except that until
loop runs as long as the expression evaluates to false.

For loop
 For loop is provided with an expression which can be iterated
over. The expression can be a string, range or an array.
 for is just syntax sugar for each method, the only difference
being the scope of the iterator variable after the block ends.
 It will throw an exception if the expression provided evaluates to
nil.
Loop modifiers

 Loop modifiers are constructs that can alter the normal flow of a
loop.
 Some of the loop modifiers are:
 break
 redo
 next
 break alters the normal flow of a loop by breaking out of the
entire loop on some condition.
 redo repeates the current iteration on some condition
 next immediately continues to the next iteration in the loop on
some condition.
Iterators

 Iterators are methods supported by collection objects.
 They return all the elements of the collection, one after the other.
 Most common type of iterators are :
 Numerical
 String
 Collection
 Numerical iterators iterate on a number and the code block gets
executed that number times.
 times
 upto
 String iterators iterate on a string literal.
 each_char
 Collection iterators iterate on collection objects.
 collect
 map
 each

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