Rails Builder

Installing Hive on linux

noreply@blogger.com (Rails builder) — Fri, 18 Jun 2010 08:27:00 +0000

Overview:

Hive is a query based, data warehouse infrastructure built on top of Hadoop that provides tools to enable easy data summarization, querying and analysis of large datasets data stored in Hadoop files. It provides a mechanism to put structure on this data and it also provides a simple query language called Hive QL which is based on SQL and which enables users familiar with SQL to query this data. At the same time, this language also allows traditional map/reduce programmers to be able to plug in their custom mappers and reducers to do more sophisticated analysis which may not be supported by the built-in capabilities of the language.

Pre-requisites:

1. Java 1.6

2. Hadoop 0.17.x to 0.20.x.

3. Ant 1.8.1

4. Subversion (SVN)

Note:

For me, I need to configure and install Hadoop 0.20.0 version.

Installation:

Download

svn co http://svn.apache.org/repos/asf/hadoop/hive/trunk hive

Using svn you can download the hive frame work from trunk

Navigate to the folder in the command shell by following command

       cd hive

      2.  Build the hive package using ant (Make sure you have installed ant)

      ant package

3.      Once if you build the jar files using ant you will find new folder structure in hive folder, navigate to below folder structure

      cd build/dist

4.      Make sure everything  build by ant is correctly by list the folder

ls

Output will be list like this

 README.txt

 bin/ (all the shell scripts)

 lib/ (required jar files)

 conf/ (configuration files)

 examples/ (sample input and query files)

Execution:

Note: Before running hive make sure you have configured and installed Hadoop 0.20.0 or any other version as per requirement

Hive use Hadoop so you need to specify the Hadoop path to hive, Hadoop folder path (which you have to download and configure ) need to make visible. You can do it by two ways

1. You can export the path for single session by following bash command

export HADOOP_HOME=hadoop-install-dir

For me it is

export HADOOP_HOME=/home/hadoop/arun/hadoop-0.20.0

Note:

Make sure HADOOP_HOME variable assigned properly is by this command

echo $HADOOP_HOME

2. You can export the path as permanent by adding it in to .bash_profile file which is shell script automatically checked first when any script executes

vi /logged_in_user_name/.bash_profile

For me it is (I logged as root)

vi /root/.bash_profile

Open the file with vi editor and add the following lines

Assigning the variable:

HADOOP_HOME=/home/hadoop/arun/hadoop-0.20.0

Make visible to all process:

export HADOOP_HOME

Note :

In addition, you must create /tmp and /user/hive/warehouse (aka hive.metastore.warehouse.dir) and set them chmod g+w in HDFS before a table can be created in Hive.

Following commands will do above creation, navigate to the Hadoop folder path (home folder ) for me it is

"/home/hadoop/arun/hadoop-0.20.0 "

And type the following commands; it will create the folder structure:

[root@master hadoop-0.20.2]# /bin/hadoop dfs -mkdir /tmp

[root@master hadoop-0.20.2]# /bin/hadoop dfs -mkdir/user/hive/warehouse

[root@master hadoop-0.20.2]# /bin/hadoop dfs -mkdir /tmp

[root@master hadoop-0.20.2]# /bin/hadoop dfs -mkdir /tmp

Basic Execution:

  Now navigate back to the hive folder downloaded and installed folder move to   Ant build  package “build/dist”, And type bin/hive the shell will open query shell in the same shell

    cd /hive_home_folder/   for me : cd /downloads/hive/

    cd build/dist

    bin/hive

  For me it is

[root@master dist]# bin/hive

Hive history file=/tmp/root/hive_job_log_root_201006181053_1733690517.txt

hive>

 Testing/Checking:

      Creating Hive table

     hive> CREATE TABLE jak (id INT, friends STRING);

  Output:

          hive> CREATE TABLE jak (id INT, friends STRING);

OK

          Time taken: 0.476 seconds

    hive>

    It will show the created Hive  table

         hive> SHOW TABLES;

Output:

hive>SHOW TABLES;

OK

jak

lists

Time taken: 0.215 seconds

hive>

Configuration:

- hive default configuration is stored in /conf/hive-default.xml

· Configuration variables can be changed by (re-)defining them in /conf/hive-site.xml

- log4j configuration is stored in /conf/hive-log4j.properties

- hive configuration is an overlay on top of hadoop - meaning the hadoop configuration variables are inherited by default.

- hive configuration can be manipulated by:

· editing hive-site.xml and defining any desired variables (including hadoop variables) in it

· from the cli using the set command (see below)

· by invoking hive using the syntax:

o $ bin/hive -hiveconf x1=y1 -hiveconf x2=y2

§ this sets the variables x1 and x2 to y1 and y2 respectively

Error logs:

Hive uses log4j for logging. By default logs are not emitted to the console by the cli. They are stored in the file: - /tmp/{user.name}/hive.log

If the user wishes - the logs can be emitted to the console by adding the arguments shown below: - bin/hive -hiveconf hive.root.logger=INFO,console

Note that setting hive.root.logger via the 'set' command does not change logging properties since they are determined at initialization time.

Error logs are very useful to debug problems. Please send them with any bugs (of which there are many!) to hive-dev@hadoop.apache.org.

Installation errors and solutions:

Note:

In installation/setup of hive you will mostly face issue on the downloading the required software to build the jar file using ant.

Error 1:

If try to build the package using ant like below

[root@master hive]# ant package

It will produce error like below

ivy-retrieve-hadoop-source:

[ivy:retrieve] :: Ivy 2.0.0-rc2 - 20081028224207 :: http://ant.apache.org/ivy/ ::

:: loading settings :: file = /master/hadoop/hive/ivy/ivysettings.xml

BUILD FAILED

/test/hive/build.xml:160: The following error occurred while executing this line:

/test/hive/build.xml:103: The following error occurred while executing this line:

/test/hive/shims/build.xml:56: The following error occurred while executing this line:

/test/hive/build-common.xml:177: impossible to resolve dependencies:

resolve failed - see output for details

Solution:

It is all about downloading file error the path is not correct so I downloaded Hadoop-0.20.0 core file and placed it ant building path as below

    cd ~/.ant/cache/hadoop/core/sources

    wget http://archive.apache.org/dist/hadoop/core/hadoop-0.20.0/hadoop-0.20.0.tar.gz

    svn update

After did this you need to change the a variable true to false in /hive/ivy/ivysettings.xml

For me hive home path is

   cd /hive/ivy

   vi ivysettings.xml

I changed the following variable to true to false (basically we tell to ant not to download file use existing file for further process)as follows

Checkmodified=”true” to checkmodified=”false”

From:

        checkmodified="true" changingPattern=".*SNAPSHOT"/>

TO:

        checkmodified="false" changingPattern=".*SNAPSHOT"/>

Now clean the ant package and build hive package for specified version of

Hadoop for me it is 0.20.0

      ant -Dhadoop.version=0.x.x clean package

For me

ant -Dhadoop.version=0.20.0 clean package

It will work fine…

Error 2:

After installing the HIVE, when we query means it will show error like

“Execution Jar: hive/lib/hive-exec-*.jar. “

Missing Hive Execution Jar

Solution:

If we do the installation (manually download and saving file in ant path) in above method some times the created of jar file (by ant) will be saved in a different location

We need to find that file and need to paste in correct path

Original/correct path is hive home folder/build/dist

For me it is cd /hive/ build/dist

Note:

If you want acces globally u need to set HIVE_HOME path refer above path setting process.

It will work fine…

Error 3:

After installing the HIVE, when we query means it will show error like “it can’t able to create JVM because of Memory HEAPSIZE is very high”

Solution:

For that we need to change the heap size in the following file

\hive\build\dist\bin\ext\util\execHiveCmd.sh

as 64 or as per your requirement

# increase the threshold for large queries

HADOOP_HEAPSIZE=64

It will work fine…

instance_eval and class_eval in ruby

noreply@blogger.com (Rails builder) — Fri, 13 Nov 2009 05:12:00 +0000

In an attempt to better understand instance_eval and class_eval, I just read Khaled’s post on Ruby reflection. It helped, and I came up with a memory crutch I can use to remember when to use each of them:

Use ClassName.instance_eval to define class methods.

Use ClassName.class_eval to define instance methods.

That’s right. Not a typo. Here are some examples, shamelessly stolen from his post:

  # Defining a class method with instance_eval
    Fixnum.instance_eval { def ten; 10; end }
    Fixnum.ten #=> 10

  # Defining an instance method with class_eval
    Fixnum.class_eval { def number; self; end }

  7.number #=> 7

I Like Stuff that’s Backwards

Why is it the reverse of what you might expect? Because Fixnum.instance_eval treats Fixnum as an instance (an instance of the Class class), thus any new functions you define can be called on that instance. So it’s equivalent to this:

  class Fixnum
  def self.ten
  10
  end
  end

  Fixnum.ten #=> 10

Fixnum.class_eval treats Fixnum as a class and executes the code in the context of that class, thus any “def” statements are treated exactly as if they were in normal code without any reflection. It’s equivalent to this:

   class Fixnum
   def number
  self
   end
    end

  7.number #=> 7

There are still some things about Ruby reflection that mystify me but at least I think I’ve got this one nailed.

Bang Methods In Ruby & Ruby Classes

noreply@blogger.com (Rails builder) — Wed, 29 Apr 2009 11:55:00 +0000

In Ruby, you can write methods whose names end in ! (exclamation point or “bang”). There’s a lot of confusion surrounding the matter of when, and why, you would want to do so.

What ! does (and does not) mean

The ! in method names that end with ! means, “This method is dangerous”—or, more precisely, this method is the “dangerous” version of an otherwise equivalent method, with the same name minus the !. “Danger” is relative; the ! doesn’t mean anything at all unless the method name it’s in corresponds to a similar but bang-less method name.

So, for example, gsub! is the dangerous version of gsub. exit! is the dangerous version of exit. flatten! is the dangerous version of flatten. And so forth.

The ! does not mean “This method changes its receiver.” A lot of “dangerous” methods do change their receivers. But some don’t. I repeat: ! does not mean that the method changes its receiver.

Don’t overuse the !
Not every !-method changes its receiver, and not every receiver-changing method ends with !. There’s Array#pop/push/shift/unshift/concat/clear, and lots of others.

Don’t add ! to your destructive (receiver-changing) methods’ names, unless you consider the changing to be “dangerous” and you have a “non-dangerous” equivalent method without the !. If some arbitrary subset of destructive methods end with !, then the whole point of ! gets distorted and diluted, and ! ceases to convey any information whatsoever.

If you want to write a destructive method and you don’t think the name conveys destruction, you might be tempted to add a ! to make it clear. That’s not a good idea. If the name of a destructive method, without a !, does not connote destruction, then the name is wrong and cannot be repaired by slapping a ! on it.

In such a case, you should create the traditional pair of methods: a non-bang method and a bang method. It’s conventional to define the non-bang method in terms of the bang one. Here’s an example involving a simplistic version of an Array#flatten_once method (it doesn’t handle nested objects other than arrays very well, but it makes the bang-point):


class Array
def flatten_once!
res = [] each do |e|
  [*e].each {|f| res <<>
The non-bang method is defined in terms of the bang method. You wouldn’t want to write an isolated method called flatten_once! without the matching non-bang version, since there’s no way to measure the “danger” except in relation to the non-dangerous method.

Danger takes many forms
Sometimes you get more than one kind of “danger” even within one bang method. Take String#gsub!. This method changes its receiver:
str = "David" str.gsub!(/$/, " Black") str # David Black It also differs from gsub (non-bang) in that if the string does not change, gsub returns a copy of the unchanged string but gsub! returns nil:
str.gsub(/xyz/, "blah") # David Black str.gsub!(/xyz/, "blah") # nil str # David Black The ! in gsub! gives you a heads-up: it warns you of danger, and that means that before you use the method, you should find out exactly how it behaves. (A simple “ri String#gsub!” should do it.

Ruby classes 

1.  Classes are themselves represented as objects.

The first thing you’ll notice when you begin to learn ruby, is that all things are objects. Ruby is a dynamic 100% object oriented language (along with lots of others, as I seemed to have forgoten). This really opens the doors to a new type of programming, called meta-programming. Meta-programming allows you to open up classes and objects as the application is running and modify them in any way needed. Even classes are objects, and thus have their own set of methods available to them. Each time you create a class you’re actually creating an object of class Class. In the code below you’ll notice that Dog has lots of methods, but it doesn’t have a method named class. Dog can call the method “class” because it is an object of type class. This gives it access to all of ruby’s class object methods. A list of available methods for class Object can be found at Ruby Central. A more updated list can be found in the Programming Ruby 2nd Edition book. If you plan doing anything beyond a recipe, or depot app, you’ll need this book!

class Dog
## lots of Dog methods that aren't def class
end

p Dog.class # => Class

2. Methods can be defined on a per-object basis
Methods can also be created for a specific instance of an object. These methods are only available to the the object named in the method call.

  dog = Object.new

def dog.bark
puts "ruff ruff"
end

dog.bark # => ruff ruff

3. You can also define per-object methods using class <<
You can also create objects by using the Object.new method. This now makes dog a certified object, and thus you are free to add methods to this object.

  dog = Object.new

class <<> ruff ruff

4. outside of methods, within a class … end block, self refers to the class
Self always references the current object. Inside of any class, self will be treated just the same as Dog (if you’re in class Dog).

  class Dog
p self # => Dog
end

5. “class methods” are simply per-object methods defined on classes
In ruby, you are able to tie a class to a particular object. Remember from tip 4 that you can replace self with Dog, and nothing about the code would change. This use of self defines a class that is based around the object self. Here, self is the class object Dog. This now allows you to add methods to class Dog. These new methods are class methods, and will be available to Dog. This means that you don’t have to create an instance of this object to call this method.

  class Dog
class <<> ruff ruff

Ruby on Rails Interview Questions

noreply@blogger.com (Rails builder) — Mon, 20 Apr 2009 06:11:00 +0000

1. Why Ruby on Rails?
Ans: There are lot of advantages of using ruby on rails
1. DRY Principal
2. Convention over Configuration
3. Gems and Plugins
4. Scaffolding
5. Pure OOP Concept

6. Rest Support

7. Rack support

8. Action Mailer

9. Rpc support

10. Rexml Support

11. etc..

2. Explain about the programming language ruby?

Ruby is the brain child of a Japanese programmer Matz. He created Ruby. It is a cross platform object oriented language. It helps you in knowing what your code does in your application. With legacy code it gives you the power of administration and organization tasks. Being open source, it did go into great lengths of development.

3. Explain about ruby names?
Classes, variables, methods, constants and modules can be referred by ruby names. When you want to distinguish between various names you can specify that by the first character of the name. Some of the names are used as reserve words which should not be used for any other purpose. A name can be lowercase letter, upper case letter, number, or an underscore, make sure that you follow the name by name characters.

4. What is the Difference between Symbol and String?

Ans: Symbol are same like string but both behaviors is different based on object_id, memory and process time (cpu time) Strings are mutable , Symbols are immutable.

Mutable objects can be changed after assignment while immutable objects can only be overwritten. For example

p "string object jak".object_id #=> 22956070

p "string object jak".object_id #=> 22956030

p "string object jak".object_id #=> 22956090

p :symbol_object_jak.object_id #=> 247378

p :symbol_object_jak.object_id #=> 247378

p :symbol_object_jak.object_id #=> 247378

p " string object jak ".to_sym.object_id #=> 247518

p " string object jak ".to_sym.object_id #=> 247518

p " string object jak ".to_sym.object_id #=> 247518

p :symbol_object_jak.to_s.object_id #=> 22704460

p :symbol_object_jak.to_s.object_id #=> 22687010

p :symbol_object_jak.to_s.object_id #=> 21141310

And also it will differ by process time

For example:

Testing two symbol values for equality (or non-equality) is faster than testing two string values for equality,

Note : Each unique string value has an associated symbol

5. What is Session and Cookies?
Ans: Session: are used to store user information on the server side.
cookies: are used to store information on the browser side or we can say client side
Session : say session[:user] = “arunkumar” it remains when the browser is not closed

6. What is request.xhr?

Ans: A request.xhr tells the controller that the new Ajax request has come, It always return Boolean values (TRUE or FALSE)

7. What is MVC? and how it Works?
Ans: MVC tends for Model-View-Controller, used by many languages like PHP, Perl, Python etc. The flow goes like this: Request first comes to the controller, controller finds and appropriate view and interacts with model, model interacts with your database and send the response to controller then controller based on the response give the output parameter to view, for Example your url is something like this:
http://localhost:3000/users/new
here users is your controller and new is your method, there must be a file in your views/users folder named new.html.erb, so once the submit button is pressed, User model or whatever defined in the rhtml form_for syntax, will be called and values will be stored into the database.

8. What things we can define in the model?
Ans: There are lot of things you can define in models few are:
1. Validations (like validates_presence_of, numeracility_of, format_of etc.)
2. Relationships(like has_one, has_many, HABTM etc.)
3. Callbacks(like before_save, after_save, before_create etc.)
4. Suppose you installed a plugin say validation_group, So you can also define validation_group settings in your model
5. ROR Queries in Sql

6. Active record Associations Relationship

9. What is ORM in Rails?
Ans: ORM tends for Object-Relationship-Model, it means that your Classes are mapped to table in the database, and Objects are directly mapped to the rows in the table.

10. How many Types of Associations Relationships does a Model has?

Ans: When you have more than one model in your rails application, you would need to create connection between those models. You can do this via associations. Active Record supports three types of associations:

one-to-one : A one-to-one relationship exists when one item has exactly one of another item. For example, a person has exactly one birthday or a dog has exactly one owner.
one-to-many : A one-to-many relationship exists when a single object can be a member of many other objects. For instance, one subject can have many books.
many-to-many : A many-to-many relationship exists when the first object is related to one or more of a second object, and the second object is related to one or many of the first object.

You indicate these associations by adding declarations to your models: has_one, has_many, belongs_to, and has_and_belongs_to_many.

11. Difference between render and redirect?
Ans:

render example:

 render :partial

 render :new

  It will render the template new.rhtml without

  calling or redirecting to the new action.



redirect example:

 redirect_to :controller => ‘users’, :action => ‘new’

  It forces the clients browser to request the

  new action.

12. What is the Difference between Static and Dynamic Scaffolding?
Ans: The Syntax of Static Scaffold is like this:
ruby script/generate scaffold User Comment
Where Comment is the model and User is your controller, So all n all static scaffold takes 2 parameter i.e your controller name and model name, whereas in dynamic scaffolding you have to define controller and model one by one.

13. How you run your Rails Application without creating database ?
Ans: You can run application by uncomment the line in environment.rb

Path => rootpath conf/ environment.rb

# Skip frameworks you're not going to use (only works if using vendor/rails)

    config.frameworks -= [ :action_web_service, :action_mailer,:active_record ]

14. How to use sql db or mysql db. without defining it in the database.yml
Ans: You can use ActiveRecord anywhere!

require 'rubygems'

require 'active_record'

ActiveRecord::Base.establish_connection({

:adapter => 'postgresql',

:user => 'foo',

:password => 'bar',

:database => 'whatever'

})

class Task <>

set_table_tame "a_legacy_thingie"

def utility_methods

update_attribute(:title, "yep")

end

end

Task.find(:first)

Etcetera. It’s ActiveRecord, you know what to do. Going wild:

ActiveRecord::Base.establish_connection(:adapter => "sqlite3",

:dbfile => ":memory:")

ActiveRecord::Schema.define(:version => 1) do

create_table :posts do |t|

t.string :title

t.text :excerpt, :body

end

end

class Post <>

validates_presence_of :title

end

Post.create(:title => "A new post!")

Post.create(:title => "Another post",

:excerpt => "The excerpt is an excerpt.")

puts Post.count

15. What are helpers and how to use helpers in ROR?
Ans: Helpers (“view helpers”) are modules that provide methods which are automatically usable in your view. They provide shortcuts to commonly used display code and a way for you to keep the programming out of your views. The purpose of a helper is to simplify the view. It’s best if the view file (RHTML/RXML) is short and sweet, so you can see the structure of the output.

16. What is Active Record?
Ans: Active Record are like Object Relational Mapping(ORM), where classes are mapped to table , objects are mapped to columns and object attributes are mapped to data in the table

17. Ruby Support Single Inheritance/Multiple Inheritance or Both?
Ans: Ruby Supports only Single Inheritance.

You can achieve Multiple Inheritance through MIXIN concept means you achieve using module by including it with classes.

18. How many types of callbacks available in ROR?
Ans:

(-) save
(-) valid
(1) before_validation
(2) before_validation_on_create
(-) validate
(-) validate_on_create
(3) after_validation
(4) after_validation_on_create
(5) before_save
(6) before_create
(-) create
(7) after_create
(8) after_save

19. What can Rails Migration do?

Ans:

create_table(name, options)
drop_table(name)
rename_table(old_name, new_name)
add_column(table_name, column_name, type, options)
rename_column(table_name, column_name, new_column_name)
change_column(table_name, column_name, type, options)
remove_column(table_name, column_name)
add_index(table_name, column_name, index_type)
remove_index(table_name, column_name)

Migrations support all the basic data types: string, text, integer, float, datetime, timestamp, time, date, binary and boolean:

string - is for small data types such as a title.
text - is for longer pieces of textual data, such as the description.
integer - is for whole numbers.
float - is for decimals.
datetime and timestamp - store the date and time into a column.
date and time - store either the date only or time only.
binary - is for storing data such as images, audio, or movies.
boolean - is for storing true or false values.

Valid column options are:

limit ( :limit => “50” )
default (:default => “blah” )
null (:null => false implies NOT NULL)

20. What is the naming conventions for methods that return a boolean result?

Ans: Methods that return a boolean result are typically named with a ending question mark. For example: def active? return true #just always returning true end

21. How do the following methods differ: @my_string.strip and @my_string.strip! ?

Ans: The strip! method modifies the variable directly. Calling strip (without the !) returns a copy of the variable with the modifications, the original variable is not altered.

22. What's the difference in scope for these two variables: @name and @@name?

Ans: @name is an instance variable and @@name is a class variable

23. What is the log that has to seen to check for an error in ruby rails?

24. What is the use of global variable $ in Ruby?

Ans: A class variable starts with an @@ sign which is immediately followed by upper or lower case letter. You can also put some name characters after the letters which stand to be a pure optional. A class variable can be shared among all the objects of a class. A single copy of a class variable exists for each and every given class.
To write a global variable you start the variable with a $ sign which should be followed by a name character. Ruby defines a number of global variables which also include other punctuation characters such as $_ and $-k.

For example: If you declare one variable as global we can access any where, where as class variable visibility only in the classÂ Example
class Test
def h
Â $a = 5
Â @b = 4
Â
while $a > 0
puts $a
$a= $a - 1
end
end
end
test = Test.new
test.h
puts $aÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â # 5
puts @bÂ Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â #nil

25. Where does the start_tabnav gets informations for tabs rendering in ruby rail?

Ans: The main Symbol let the start_tabnav method know to look for a special MainTabnav class where all the magic happens

26. What is the Install rail package?

Ans: There are several packages that you can download and install. The prebuilt Rails installer called Install rail which currently is only for Windows

27. What is the log that has to seen to check for an error in ruby rails?

Ans: Rails will report errors from Apache in log/apache.log and errors from the Ruby code in log/development.log. If you're having a problem, do have a look at what these logs are saying. On Unix and Mac OS X you may run tail -f log/development.log in a separate terminal to monitor your application's execution.

28. What is the use of super in ruby rails?
Ans: Ruby uses the super keyword to call the superclass (Parent class) implementation of the current method

29. What is the difference between nil and false in ruby?
Ans: False is a boolean datatype, Nil is not a data type it have object_id 4

30. How is class methods defined in Ruby?
Ans: A:def self.methodname
--------
--------
end
or
def classname.methodname
--------
--------
end

31. How is object methods defined in Ruby?
Ans:

class jak

def method1

--------
--------
end

end

obj=jak.new

It is single object
def obj.object_method_one
--------
--------
end

obj.Send(object_method_every)

It will be created every for every object creation

32. What are the priority of operators available in Ruby ?
Ans: Something that used in an expression to manipulate objects such as + (plus), - (minus), * (multiply), and / (divide). You can also use operators to do comparisons,such as with <, >, and &&. The priority is based on "BODMAS"

33. What are the looping structures available in Ruby?

Ans: for..in
untill..end
while..end
do..end

Note: You can also use each to iterate a array as loop not exactly like loop

34. What are the object-oriented programming features supported by Ruby and how multiple inheritance supported in ?

Ans: Classes,Objects,Inheritance,Singleton methods,polymorphism(accomplished by over riding and overloading) are some oo concepts supported by ruby. Multiple inheritance supported using Mixin concept.

35. What is the scope of a local variable in Ruby and define it scope ?

Ans: A new scope for a local variable is introduced in the toplevel, a class (module) definition, a method defintion. In a procedure block a new scope is introduced but you can access to a local variable outside the block.
The scope in a block is special because a local variable should be localized in Thread and Proc objects.

36. How is an enumerator iterator handled in Ruby?

Ans: Iterator is handled using keyword 'each' in ruby.
For example
number=[1,2,3]
then we can use iterator as
number.each do |i|
puts i
end
Above prints the values of an array $no which is accomplished using iterator.

37. How is visibility of methods changed in Ruby (Encapsulation)?

Ans: By applying the access modifier : Public , Private and Protected access Modifier

38. What is the use of load,require, auto_load,require_relative in Ruby?

Ans: A method that loads and processes the Ruby code from a separate file, including whatever classes, modules, methods, and constants are in that file into the current scope. load is similar, but rather than performing the inclusion operation once, it reprocesses the code every time load is called.

auto_load - Whenever the interpreter call the method that time only it will initiate the method in hat file.

require_relative - It it to load local folder files.

A to Z DOS Command-Line Tricks for XP

noreply@blogger.com (Rails builder) — Tue, 20 Jan 2009 12:37:00 +0000

Typing DOS commands on the Windows Command Line prompt is a most efficient and faster way of doing things in Windows XP. Here's a run-down of the most useful DOS commands available in Windows XP. Some of these DOS commands even do not have an visual alternative.

DOS Command-line tools must be run at the prompt of the Cmd.exe command interpreter. To open Command Prompt, click Start, click Run, type cmd, and then click OK.

ipconfig - Windows IP configuration
Useful for troubleshooting your internet connection. Displays the current IP address of your computer and the DNS server address. If you call your ISP for reporting a bad internet connection, he will probably ask you to run ipconfig.

fc - Free BeyondCompare in XP
FC is an advanced DOS Command that compares two files and displays the differences between them. Though the file comparison results are not as interactive as BeyondCompare or Altova DiffDog, fc is still very useful. You can even set fc to resynchronize the files after finding a mismatch.

type - open text files sans Notepad
Similar to Unix cat command, Type is my favorite DOS command for displaying the contents of a text files without modifying them. When used in combination with more switch, type splits the contents of lengthy text files into multiple pages. Avoid using the type command with binary files or you'll hear alien PC beeps and see some greek characters on your PC.

ping - Say hello to another computer
Ping network command followed by the web-address or IP address tells you about the health of the connection and whether the other party is responding to your handshake request. Ping tool can also be used to convert the web address to a physical IP address.

tree - visual directory structure
You often need to take prints of your physical directory structure but XP has no simple "visual" commands for printing directory contents. Here, try the Tree DOS command and redirect the output to a text file.

tree > mydirectory.txt
print mydirectory.txt

attrib - make hidden files visible
Attrib lets you change attributes of System files and even hidden files. This is great for troubleshooting Windows XP. Say your XP doesn't boot ever since you edited that startup boot.ini file (Hidden), use attrib to remove the Hidden attibute and edit the file using EDIT dos command.

assoc - which program will open that .xyz file
The assoc DOS command can be used to either isplay or even modify the file name extension associations. The command assoc .htm will quickly tell you the name of your default web browser (see picture)

move - more flexible than copy-paste
Say you got a lot of XLS and DOC files in you MyDocuments folder and want to move only those XLS files that have their name ending with 2006. In XP Explorer, you have to manually select each file and then cut-paste to another folder. However, the DOS move command make things much simpler. Just type the following at the command prompt:
move *2006.xls c:\2006Reports\

find - advanced file search with filter
Find is the most powerful DOS command and even more useful than the Windows Desktop Search tool or the Windows Find Wizard. The find command searches for a specific string of text in a file or files. After searching the specified file or files, find displays any lines of text that contain the specified string.

To search your hard disk to find and display the file names on drive C: that contain the string "Google" use the pipe (|) to direct the results of a dir command to find as follows:
dir c:\ /s /b | find "Google"

Quick tip - Drag to avoid typing: When your command acts on a file or folder, you must type the path to that folder after the command. You can save typing time by dragging the file or folder from Windows Explorer into the command window.

To view help at the command-line, at the command prompt, type the following:
CommandName /?

Run Commands

start> run and enter the following commands:

appwiz.cpl -- Used to run Add/Remove wizard

Calc --Calculator

Cfgwiz32 --ISDN Configuration Wizard

Charmap --Character Map

Chkdisk --Repair damaged files

Cleanmgr --Cleans up hard drives

Clipbrd --Windows Clipboard viewer

Control --Displays Control Panel

Cmd --Opens a new Command Window

Control mouse --Used to control mouse properties

Dcomcnfg --DCOM user security

Debug --Assembly language programming tool

Defrag --Defragmentation tool

Drwatson --Records programs crash & snapshots

Dxdiag --DirectX Diagnostic Utility

Explorer --Windows Explorer

Fontview --Graphical font viewer

Fsmgmt.msc -- Used to open shared folders

Firewall.cpl -- Used to configure windows firewall

Ftp -ftp.exe program

Hostname --Returns Computer's name

Hdwwiz.cpl -- Used to run Add Hardware wizard

Ipconfig --Displays IP configuration for all network adapters

Logoff -- Used to logoff the computer

MMC --Microsoft Management Console

Msconfig --Configuration to edit startup files

Mstsc -- Used to access remote desktop

Mrc -- Malicious Software Removal Tool

Msinfo32 --Microsoft System Information Utility

Nbtstat --Displays stats and current connections using NetBIOS over TCP/IP

Netstat --Displays all active network connections

Nslookup--Returns your local DNS server

Osk ---Used to access on screen keyboard

Perfmon.msc -- Used to configure the performance of Monitor.

Ping --Sends data to a specified host/IP

Powercfg.cpl -- Used to configure power option

Regedit --Registry Editor

Regwiz -- Registration wizard

Sfc /scannow -- System File Checker

Sndrec32 --Sound Recorder

Shutdown -- Used to shutdown the windows

Spider -- Used to open spider solitaire card game

Sfc / scannow -- Used to run system file checker utility.

Sndvol32 --Volume control for soundcard

Sysedit -- Edit system startup files

Taskmgr --Task manager

Telephon.cpl -- Used to configure modem options.

Telnet --Telnet program

Tracert --Traces and displays all paths required to reach an internet host

Winchat -- Used to chat with Microsoft

Wmplayer -- Used to run Windows Media player

Wab -- Used to open Windows address Book.

WinWord -- Used to open Microsoft word

Winipcfg --Displays IP configuration

Winver -- Used to check Windows Version

Wupdmgr --Takes you to Microsoft Windows Update

Write -- Used to open WordPad

An A-Z Index of the Windows XP command line

   ADDUSERS Add or list users to/from a CSV file
  ARP      Address Resolution Protocol
~ ASSOC    Change file extension associations
  ASSOCIAT One step file association
  AT       Schedule a command to run at a later time
  ATTRIB   Change file attributes
b
  BOOTCFG  Edit Windows boot settings
  BROWSTAT Get domain, browser and PDC info
c
  CACLS    Change file permissions
~ CALL     Call one batch program from another
~ CD       Change Directory - move to a specific Folder
  CHANGE   Change Terminal Server Session properties
  CHKDSK   Check Disk - check and repair disk problems
  CHKNTFS  Check the NTFS file system
  CHOICE   Accept keyboard input to a batch file
  CIPHER   Encrypt or Decrypt files/folders
  CleanMgr Automated cleanup of Temp files, recycle bin
  CLEARMEM Clear memory leaks
  CLIP     Copy STDIN to the Windows clipboard.
~ CLS      Clear the screen
  CLUSTER  Windows Clustering
  CMD      Start a new CMD shell
~ COLOR    Change colors of the CMD window
  COMP     Compare the contents of two files or sets of files
  COMPACT  Compress files or folders on an NTFS partition
  COMPRESS Compress individual files on an NTFS partition
  CON2PRT  Connect or disconnect a Printer
  CONVERT  Convert a FAT drive to NTFS.
~ COPY     Copy one or more files to another location
  CSCcmd   Client-side caching (Offline Files)
  CSVDE    Import or Export Active Directory data
d
~ DATE     Display or set the date
  Dcomcnfg DCOM Configuration Utility
  DEFRAG   Defragment hard drive
~ DEL      Delete one or more files
  DELPROF  Delete NT user profiles
  DELTREE  Delete a folder and all subfolders
  DevCon   Device Manager Command Line Utility
~ DIR      Display a list of files and folders
  DIRUSE   Display disk usage
  DISKCOMP Compare the contents of two floppy disks
  DISKCOPY Copy the contents of one floppy disk to another
  DISKPART Disk Administration
  DNSSTAT  DNS Statistics
  DOSKEY   Edit command line, recall commands, and create macros
  DSADD    Add user (computer, group..) to active directory
  DSQUERY  List items in active directory
  DSMOD    Modify user (computer, group..) in active directory
e
~ ECHO     Display message on screen
~ ENDLOCAL End localisation of environment changes in a batch file
~ ERASE    Delete one or more files
~ EXIT     Quit the current script/routine and set an errorlevel.
  EXPAND   Uncompress files
  EXTRACT  Uncompress CAB files
f
  FC       Compare two files
  FIND     Search for a text string in a file
  FINDSTR  Search for strings in files
~ FOR /F   Loop command: against a set of files
~ FOR /F   Loop command: against the results of another command
~ FOR      Loop command: all options Files, Directory, List
  FORFILES Batch process multiple files
  FORMAT   Format a disk
  FREEDISK Check free disk space (in bytes)
  FSUTIL   File and Volume utilities
  FTP      File Transfer Protocol
~ FTYPE    Display or modify file types used in file extension associations
g
  GLOBAL   Display membership of global groups
~ GOTO     Direct a batch program to jump to a labelled line
h
  HELP     Online Help
i
~ IF       Conditionally perform a command
  IFMEMBER Is the current user in an NT Workgroup
  IPCONFIG Configure IP
k
  KILL     Remove a program from memory
l
  LABEL    Edit a disk label
  LOCAL    Display membership of local groups
  LOGEVENT Write text to the NT event viewer.
  LOGOFF   Log a user off
  LOGTIME  Log the date and time in a file
m
  MAPISEND Send email from the command line
  MBSAcli  Baseline Security Analyzer.
  MEM      Display memory usage
~ MD       Create new folders
  MKLINK   Create a symbolic link (linkd)
  MODE     Configure a system device
  MORE     Display output, one screen at a time
  MOUNTVOL Manage a volume mount point
~ MOVE     Move files from one folder to another
  MOVEUSER Move a user from one domain to another
  MSG      Send a message
  MSIEXEC  Microsoft Windows Installer
  MSINFO   Windows NT diagnostics
  MSTSC    Terminal Server Connection (Remote Desktop Protocol)
  MUNGE    Find and Replace text within file(s)
  MV       Copy in-use files
n
  NET      Manage network resources
  NETDOM   Domain Manager
  NETSH    Configure network protocols
  NETSVC   Command-line Service Controller
  NBTSTAT  Display networking statistics (NetBIOS over TCP/IP)
  NETSTAT  Display networking statistics (TCP/IP)
  NOW      Display the current Date and Time
  NSLOOKUP Name server lookup
  NTBACKUP Backup folders to tape
  NTRIGHTS Edit user account rights
p
~ PATH     Display or set a search path for executable files
  PATHPING Trace route plus network latency and packet loss
~ PAUSE    Suspend processing of a batch file and display a message
  PERMS    Show permissions for a user
  PERFMON  Performance Monitor
  PING     Test a network connection
~ POPD     Restore the previous value of the current directory saved by PUSHD
  PORTQRY  Display the status of ports and services
  PRINT    Print a text file
  PRNCNFG  Display, configure or rename a printer
  PRNMNGR  Add, delete, list printers set the default printer
~ PROMPT   Change the command prompt
  PsExec     Execute process remotely
  PsFile     Show files opened remotely
  PsGetSid   Display the SID of a computer or a user
  PsInfo     List information about a system
  PsKill     Kill processes by name or process ID
  PsList     List detailed information about processes
  PsLoggedOn Who's logged on (locally or via resource sharing)
  PsLogList  Event log records
  PsPasswd   Change account password
  PsService  View and control services
  PsShutdown Shutdown or reboot a computer
  PsSuspend  Suspend processes
~ PUSHD    Save and then change the current directory
q
  QGREP    Search file(s) for lines that match a given pattern.
r
  RASDIAL  Manage RAS connections
  RASPHONE Manage RAS connections
  RECOVER  Recover a damaged file from a defective disk.
  REG      Registry: Read, Set, Export, Delete keys and values
  REGEDIT  Import or export registry settings
  REGSVR32 Register or unregister a DLL
  REGINI   Change Registry Permissions
~ REM      Record comments (remarks) in a batch file
~ REN      Rename a file or files.
  REPLACE  Replace or update one file with another
~ RD       Delete folder(s)
  RMTSHARE Share a folder or a printer
  ROBOCOPY Robust File and Folder Copy
  ROUTE    Manipulate network routing tables
  RUNAS    Execute a program under a different user account
  RUNDLL32 Run a DLL command (add/remove print connections)
s
  SC       Service Control
  SCHTASKS Create or Edit Scheduled Tasks
  SCLIST   Display NT Services
~ SET      Display, set, or remove environment variables
~ SETLOCAL Control the visibility of environment variables
  SETX     Set environment variables permanently
  SHARE    List or edit a file share or print share
~ SHIFT    Shift the position of replaceable parameters in a batch file
  SHORTCUT Create a windows shortcut (.LNK file)
  SHOWGRPS List the NT Workgroups a user has joined
  SHOWMBRS List the Users who are members of a Workgroup
  SHUTDOWN Shutdown the computer
  SLEEP    Wait for x seconds
  SOON     Schedule a command to run in the near future
  SORT     Sort input
~ START    Start a program or command in a separate window.
  SU       Switch User
  SUBINACL Edit file and folder Permissions, Ownership and Domain
  SUBST    Associate a path with a drive letter
  SYSTEMINFO List system configuration
t
  TASKLIST List running applications and services
  TASKKILL Remove a running process from memory
~ TIME     Display or set the system time
  TIMEOUT  Delay processing of a batch file
~ TITLE    Set the window title for a CMD.EXE session
  TLIST    Task list with full path
  TOUCH    Change file timestamps   
  TRACERT  Trace route to a remote host
  TREE     Graphical display of folder structure
~ TYPE     Display the contents of a text file
u
  USRSTAT  List domain usernames and last login
v
~ VER      Display version information
~ VERIFY   Verify that files have been saved
~ VOL      Display a disk label
w
  WHERE    Locate and display files in a directory tree
  WHOAMI   Output the current UserName and domain
  WINDIFF  Compare the contents of two files or sets of files
  WINMSD   Windows system diagnostics
  WINMSDP  Windows system diagnostics II
  WMIC     WMI Commands
x
  XCACLS   Change file permissions
  XCOPY    Copy files and folders
~ ::       Comment / Remark

Commands marked ~ are Internal commands only available within the CMD shell.

20 Things you didn't know about Windows XP -Jak

noreply@blogger.com (Rails builder) — Thu, 01 Jan 2009 12:21:00 +0000

You've read the reviews and digested the key feature enhancements and operational changes. Now it's time to delve a bit deeper and uncover some of Windows XP's secrets.

1. It boasts how long it can stay up. Whereas previous versions of Windows were coy about how long they went between boots, XP is positively proud of its stamina. Go to the Command Prompt in the Accessories menu from the All Programs start button option, and then type 'systeminfo'. The computer will produce a lot of useful info, including the uptime. If you want to keep these, type 'systeminfo > info.txt'. This creates a file called info.txt you can look at later with Notepad. (Professional Edition only).

2. You can delete files immediately, without having them move to the Recycle Bin first. Go to the Start menu, select Run... and type 'gpedit.msc'; then select User Configuration, Administrative Templates, Windows Components, Windows Explorer and find the Do not move deleted files to the Recycle Bin setting. Set it. Poking around in gpedit will reveal a great many interface and system options, but take care -- some may stop your computer behaving as you wish. (Professional Edition only).

3. You can lock your XP workstation with two clicks of the mouse. Create a new shortcut on your desktop using a right mouse click, and enter 'rundll32.exe user32.dll,LockWorkStation' in the location field. Give the shortcut a name you like. That's it -- just double click on it and your computer will be locked. And if that's not easy enough, Windows key + L will do the same.

4. XP hides some system software you might want to remove, such as Windows Messenger, but you can tickle it and make it disgorge everything. Using Notepad or Edit, edit the text file /windows/inf/sysoc.inf, search for the word 'hide' and remove it. You can then go to the Add or Remove Programs in the Control Panel, select Add/Remove Windows Components and there will be your prey, exposed and vulnerable.

5. For those skilled in the art of DOS batch files, XP has a number of interesting new commands. These include 'eventcreate' and 'eventtriggers' for creating and watching system events, 'typeperf' for monitoring performance of various subsystems, and 'schtasks' for handling scheduled tasks. As usual, typing the command name followed by /? will give a list of options -- they're all far too baroque to go into here.

6. XP has IP version 6 support -- the next generation of IP. Unfortunately this is more than your ISP has, so you can only experiment with this on your LAN. Type 'ipv6 install' into Run... (it's OK, it won't ruin your existing network setup) and then 'ipv6 /?' at the command line to find out more. If you don't know what IPv6 is, don't worry and don't bother.

7. You can at last get rid of tasks on the computer from the command line by using 'taskkill /pid' and the task number, or just 'tskill' and the process number. Find that out by typing 'tasklist', which will also tell you a lot about what's going on in your system.

8. XP will treat Zip files like folders, which is nice if you've got a fast machine. On slower machines, you can make XP leave zip files well alone by typing 'regsvr32 /u zipfldr.dll' at the command line. If you change your mind later, you can put things back as they were by typing 'regsvr32 zipfldr.dll'.

9. XP has ClearType -- Microsoft's anti-aliasing font display technology -- but doesn't have it enabled by default. It's well worth trying, especially if you were there for DOS and all those years of staring at a screen have given you the eyes of an astigmatic bat. To enable ClearType, right click on the desktop, select Properties, Appearance, Effects, select ClearType from the second drop-down menu and enable the selection. Expect best results on laptop displays. If you want to use ClearType on the Welcome login screen as well, set the registry entry HKEY_USERS/.DEFAULT/Control Panel/Desktop/FontSmoothingType to 2.

10. You can use Remote Assistance to help a friend who's using network address translation (NAT) on a home network, but not automatically. Get your pal to email you a Remote Assistance invitation and edit the file. Under the RCTICKET attribute will be a NAT IP address, like 192.168.1.10. Replace this with your chum's real IP address -- they can find this out by going to www.whatismyip.com -- and get them to make sure that they've got port 3389 open on their firewall and forwarded to the errant computer.

11. You can run a program as a different user without logging out and back in again. Right click the icon, select Run As... and enter the user name and password you want to use. This only applies for that run. The trick is particularly useful if you need to have administrative permissions to install a program, which many require. Note that you can have some fun by running programs multiple times on the same system as different users, but this can have unforeseen effects.

12. Windows XP can be very insistent about you checking for auto updates, registering a Passport, using Windows Messenger and so on. After a while, the nagging goes away, but if you feel you might slip the bonds of sanity before that point, run Regedit, go to HKEY_CURRENT_USER/Software/Microsoft/Windows/Current Version/Explorer/Advanced and create a DWORD value called EnableBalloonTips with a value of 0.

13. You can start up without needing to enter a user name or password. Select Run... from the start menu and type 'control userpasswords2', which will open the user accounts application. On the Users tab, clear the box for Users Must Enter A User Name And Password To Use This Computer, and click on OK. An Automatically Log On dialog box will appear; enter the user name and password for the account you want to use.

14. Internet Explorer 6 will automatically delete temporary files, but only if you tell it to. Start the browser, select Tools / Internet Options... and Advanced, go down to the Security area and check the box to Empty Temporary Internet Files folder when browser is closed.

15. XP comes with a free Network Activity Light, just in case you can't see the LEDs twinkle on your network card. Right click on My Network Places on the desktop, then select Properties. Right click on the description for your LAN or dial-up connection, select Properties, then check the Show icon in notification area when connected box. You'll now see a tiny network icon on the right of your task bar that glimmers nicely during network traffic.

16. The Start Menu can be leisurely when it decides to appear, but you can speed things along by changing the registry entry HKEY_CURRENT_USER/Control Panel/Desktop/MenuShowDelay from the default 400 to something a little snappier. Like 0.

17. You can rename loads of files at once in Windows Explorer. Highlight a set of files in a window, then right click on one and rename it. All the other files will be renamed to that name, with individual numbers in brackets to distinguish them. Also, in a folder you can arrange icons in alphabetised groups by View, Arrange Icon By... Show In Groups.

18. Windows Media Player will display the cover art for albums as it plays the tracks -- if it found the picture on the Internet when you copied the tracks from the CD. If it didn't, or if you have lots of pre-WMP music files, you can put your own copy of the cover art in the same directory as the tracks. Just call it folder.jpg and Windows Media Player will pick it up and display it.

19. Windows key + Break brings up the System Properties dialogue box; Windows key + D brings up the desktop; Windows key + Tab moves through the taskbar buttons.

20. The next release of Windows XP, codenamed Longhorn, is due out late next year or early 2003 and won't be much to write home about. The next big release is codenamed Blackcomb and will be out in 2003/2004.