Lets Quick Start With Values

#values

"string"     #this is string, strings can be double or single quoted
1            #this is number
4.0          # this is float
true         #this is boolean
false        #the other boolean
nil          #another value, like boolean but not same
/regex/      #regexs are builtin and readily available
[1,2,3]      # arrays

#hash can have anything as key and value
{:a => "a", :b => "b", "c" => c }

More Values

#common expressions
true == false                  #=> false
false !=  true                 #=> true
"somestring" =~ /string$/      #=> true (as it matches)not 
not true                       #=> false
false or true                  #=> true
true and false                 #=> false

require "time"                 #this is how we import a library
puts "string"                  #print string
now = Time.now()               #assign value
puts "current time is #{time}" #string interpolation

Loops,Iteration

3.times do
  puts "something"
end

for i in 0..9 do
    puts "#{i}"
end

i = 0 ; while i < 10 do
    i = i + 1; puts i
end

i = 0; until i > 10 do 
    i = i + 1; puts i
end

Loops,Iteration

array = ["this","is","an","array"]

# ugly way
for i in 0..array.length do
    puts array[i]
end

# better way
array.each do |v|
    puts v
end

hash = {:a => "a" , :b => "b"}
hash.each do |k,v|
    puts k,v
end

Loops,Iteration

# infinite loop, use with caution
loop do
  print "Input: "
  line = gets
  break if !line or line =~ /^qQ/
end

# generate valued loop, something like for
(0..10).each do |v| 
  next if v < 5
  puts v
end

Flow Control

x = 1

if x == 2
  puts "x is 2"
elsif x == 1
  puts "x is 1"
else 
  puts "x is neither one 1 or 2"
end

y = 6 if x == 1               # we can use if in assignment statement

Flow Control

unless false                  # unless is short for if not
    puts "this will run"
end

y = 7 unless defined? (y)     #we can use unless in assignment statement

# assign using if else block
y = if someexpression()
       somefunction()
    else
       someotherfunction()
    end

Flow Control

test = somefunc()

case test
    when test.is_a? String
        puts "test is string"
    when test.is_a? FixNum
        puts "test is a integer"
    when test.is_a? Float
        puts "test is a floating point number"
    else
        puts "can't identify what test is"
end

Ruby Fundamentals

Almost Everything in ruby is an object, lets examine using reflection api

3.class              #objects are instance of a class
3.methods            #objects have methods
3.class.class        #classes inherits Class class

3.class.ancestors    #classes have ancestors
3.is_a? Object       #objects are instance of object class
3.is_a? Class        #But instances of a class are not class

Class.is_a? Object   #class Class inherits Object class

3.send("abs")        #You can send methods to objects by creating strings 

Ruby Fundamentals..

Declaring class

class Someclass
  @@var1 = 0         #a class variable shared across different instances of class
  def initialize(v1) #initialize instance variable, different for each instance
    @v1 = v1
  end
  def instancemethod(v2)    #instance method
    puts @v1 + v2       #v2 is a local variable for functino
  end
  def self.classmethod(v3)
    @@var1 += v3
  end
end
v = Someclass.new 1 ; v.instancemethod(5)
Someclass.classmethod(6)

Ruby Fundamentals

Extend existing class

 class Hash
   def inverse
     self.reduce({}){ |h,(k,v)| (h[v] ||=[]) << k; h}
  end
end

k = {"a" => 1, "b" => 2, "c" => 1}
k.inverse   #=> {1 => ["a","c"],2 => "b"}

Calling external code

k = `ls -alh /home/`      # gives standard output as string
y = %x[ls -alh /home]     # does the same thing as above

$?.exitstatus             # will give exitcode of the last command ran
$?.pid                    #gives process id of last command ran


val = "/home/"

dirs = `ls #{val}`


dirs.split("\n").grep(/somefile/) 

Functional Programming

• Makes program easy to reason about
• Takes a little getting used to
• Fast, concise logic
• Higher order functions
• Very useful when using ruby collections

Functional programming..

#Higher order function examples

$dates = (0..3).to_a.map{ |n| Time.now - 86400 * n }.map {|n| n.strftime "%d-%m-%Y"}

$hosts = Dir.entries("/data/hosts/").select {|v| v =~ /.net|.in/}

$hosts = Dir.entries("/data/hosts/").select {|v| v =~ /.net|.in/}.reject { |v| v =~ /bll-2/}