Vidul Nikolaev Petrov

n = Time.now

(n.at_end_of_week - n.at_beginning_of_week) / (24 * 3600)

# 6.99998842592593

>> Time.now.at_beginning_of_week
=> Mon Aug 04 00:00:00 +0300 2008

>> Time.now.at_end_of_week
=> Sun Aug 10 23:59:59 +0300 2008

module Rails

  empty_and_nil = %q{def empty_and_nil; self.empty?? nil : self end}

  Array.send :class_eval, empty_and_nil
  Hash.send  :class_eval, empty_and_nil

end

# if the birthdate is 1978-12-03

Time.gm(1978, 12, 3).strftime("%a") 
Time.gm(1978, 12, 3).strftime("%A") 

# the weekday day is "Sun" (%a), "Sunday" (%A)

class Array
  def empty_and_nil
    self.empty?? nil : self
  end
end

result = [1,2,3].empty_and_nil # [1, 2, 3]
result = [].empty_and_nil        # nil

nil == false => false
nil.nil?        => true
false.nil?     => false
true.nil?      => false

if !nil && !false
  puts 'true'
end

if nil.nil? && !true.nil?
  puts 'true'
end

>> TrueClass.ancestors
=> [TrueClass, Object, Kernel]
>> FalseClass.ancestors
=> [FalseClass, Object, Kernel]
>> NilClass.ancestors
=> [NilClass, Object, Kernel]

alias _rmdir_empty='rmdir * 2>/dev/null'

mt = Array.new(10) { |e| Hash.new { |h,k| h[k] = k * e } }

mt[1][2] => 2
mt[2][2] => 4
mt[5][4] => 20
mt[9][5] => 45

# decimal to binary
alias d2b='ruby -e "puts ARGV.first.to_i.to_s(2)"'
# decimal to hexademical
alias d2h='ruby -e "puts ARGV.first.to_i.to_s(16)"'
# decimal to octal
alias d2o='ruby -e "puts ARGV.first.to_i.to_s(8)"'

# binary to decimal
alias b2d='ruby -e "puts eval(%q|0b| + ARGV.first)"'
# binary to hexademical
alias b2h='ruby -e "puts eval(%q|0b| + ARGV.first).to_s(16)"'
# binary to octal
alias b2o='ruby -e "puts eval(%q|0b| + ARGV.first).to_s(8)"'

# hexademical to decimal
alias h2d='ruby -e "puts eval(%q|0x| + ARGV.first)"'
# hexademical to binary
alias h2b='ruby -e "puts eval(%q|0x| + ARGV.first).to_s(2)"'
# hexademical to octal
alias h2o='ruby -e "puts eval(%q|0x| + ARGV.first).to_s(8)"'

# octal to decimal
alias o2d='ruby -e "puts eval(%q|0o| + ARGV.first)"'
# octal to binary
alias o2b='ruby -e "puts eval(%q|0o| + ARGV.first).to_s(2)"'
# octal to hexademical
alias o2h='ruby -e "puts eval(%q|0o| + ARGV.first).to_s(16)"'

require 'rubygems'
require 'google_translate'

tr = Google::Translate.new

# from English to German
tr.translate :from => "en", :to => "de", :text => "Hello, World!"
 => Hallo, Welt!

# from English to Spanish
tr.translate :from => "en", :to => "es", :text => "Hello, World!"
 => Hola, Mundo!

# WWW::Mechanize constructor usage
tr = Google::Translate.new { |agent| agent.user_agent_alias = 'Mac Safari' }