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To compress a folder

tar -zcvf tar-archive-name.tar.gz source-folder-name

To un-compress a tar.gz

tar -zxvf tar-archive-name.tar.gz

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class MyColor
  attr_accessor :red, :blue, :green, :alpha
  def initialize(args)
    @red = args[:red]
    @blue = args[:blue]
    @green = args[:green]
    @alpha = args[:alpha] || 1
  end
  def distance(color)   
    red_diff = self.red - color.red

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User.select(:first,:email).group(:first,:email).having("count(*) > 1").count

#{[nil, nil]=>512,
# ["Joe", "test@test.com"]=>23,
# ["Jim", "email2@gmail.com"]=>36,
# ["John", "email3@gmail.com"]=>21}

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# I was trying to connect my Edimax Wifi dongle to my raspberrypi
# I tried configuring it using the following llink
# http://www.savagehomeautomation.com/projects/raspberry-pi-installing-the-edimax-ew-7811un-usb-wifi-adapte.html
# but Edimax would not connect to my router
# after refering to the following link
# http://www.cyberciti.biz/faq/debian-linux-wpa-wpa2-wireless-wifi-networking/
# I was able to connect make the raspberrypi connect to the router.


# this is how my /etc/network/interfaces looks like on my raspberrypi

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Multiple SSH Keys settings for different github account

create different public key

create different ssh key according the article Mac Set-Up Git

$ ssh-keygen -t rsa -C "your_email@youremail.com"

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class Smokers < ActiveRecord:: Base
  belongs_to :heart_failure_statistics
  has_many :cigarettes
  attr_accessor :mins_since_last_puff

  before_validation :check_cigarettes

  def smoke?
    if mins_since_last_puff >= 60
      print("Smoke?")

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http://kvz.io/blog/2013/01/16/vagrant-tip-keep-virtualbox-guest-additions-in-sync/

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http://stackoverflow.com/questions/22922891/vagrant-ssh-authentication-failure/23554973#23554973

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 du -chs *

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  \l - to list all the databases
  \connect <dbname> - connect to the db
  \dt - list all the tables in the current DB