examples

#ex16_readingwriting.txt#

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+# Exercise 16 Reading and Writign Files

BookInStock.rb

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+
+class BookInStock
+  attr_reader   :isbn
+  attr_accessor :price
+
+  def isbn=(isbn)
+    @isbn = isbn
+  end
+
+  def price=(price)
+    @price = price
+  end
+
+  def initialize(isbn, price)
+    raise(ArgumentError, "ISBN should not be empty") if isbn==''
+    raise ArgumentError.new("Price should not be empty")  if price == ''
+    @isbn = isbn
+    @price = Float(price)
+    raise ArgumentError.new("Price has to be bigger than 0") if price <= 0
+  end
+
+  def price_as_string
+    return sprintf("$%2.2f", price)
+  end
+end

binary_multiple_of_4.rb

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+
+  def hello(name)
+    hellostring="Hello, "
+    return hellostring += name
+  end
+
+
+
+  def starts_with_consonant?(s)
+    if /[aeiouAEIOU*]/.match(s[0])
+      return false
+    elsif /0-9*/.match(s[0])
+      return false
+    elsif /[^a-zA-Z0-9.*]/.match(s)
+      return false
+    elsif /^$/.match(s)
+      return false
+    else
+      return true
+    end
+  end
+
+  def binary_multiple_of_4?(s)
+    is = s.to_i
+    if s == "0"
+      return true
+    elsif /[a-zA-Z^$3-9*]/.match(s)
+      return false
+    else
+      if /^[10]*00$/.match(s) && is % 2 == 0
+        return true
+      else
+        return false
+      end
+    end
+  end
+

ex1.rb

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+puts "Hello World!"
+puts "Hello Again"
+puts "I like typing this."
+puts "This is fun."
+puts "Yay! Printing."
+puts "I'd much rather you 'not'."
+puts 'I "said" do not touch this.'
+puts "Look another line."
+puts 'Look another line.'
+# puts 'this makes the line a comment'

ex10_cat.rb

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+tabby_cat = "\tI'm tabbed in."
+persian_cat = "I'm split\non a line."
+backslash_cat = "I'm \\ a \\ cat."
+
+fat_cat = <<MY_HEREDOC
+I'll do a list:
+\t* Cat food
+\t* Fishies
+\t* Catnip\n\t* Grass
+MY_HEREDOC
+
+puts tabby_cat
+puts persian_cat
+puts backslash_cat
+puts fat_cat
+
+poppy_cat = "This string has a quote: \". As you can see, it is escaped"
+
+puts poppy_cat

ex11_questions.rb

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+# chomp removes newline is a string method
+# gets returns a string
+
+print "How old are you? "
+age = gets.chomp()
+print  "How tall are you? "
+height = gets.chomp()
+print "How much do you weigh? "
+weight = gets.chomp()
+
+puts "So, you're #{age} years old, #{height} tall and #{weight} heavy."

ex11_questions.rb~

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+# Exercise 11: Asking Questions
+# chomp removes newline is a string method
+# gets returns a string
+
+print "How old are you? "
+age = gets.chomp()
+print  "How tall are you? "
+height = gets.chomp()
+print "How much do you weigh? "
+weight = gets.chomp()
+
+puts "So, you're #{age} years old, #{height} tall and #{weight} heavy."

ex12_libraries.rb

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+# Exercise 12: Libraries
+# require runs another file
+# wont require the same file twice
+# good if you just want to use a module
+
+# include adds all the methods from another file
+# allows you to extend classes with other modules
+
+# load lets you execute methods
+
+require 'open-uri'
+
+open("http://www.ruby-lang.org/en") do |f|
+  f.each_line {|line| p line}
+  puts f.base_uri # <URI::HTTP:0x40e6df2 URL:http://www.ruby-lang.org/en/>
+  puts f.content_type # "Text/html"
+  puts f.charset # "iso-8859-1"
+  puts f.content_encoding # []
+  puts f.last_modified # Thu Dec 05 02:45:02 UTC 2002
+end

ex13_parameters.rb

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+# Exercise 13: Parameters, Unpacking, Variables
+# ARGV is the argument variable
+# ARGV is a constant. It holds the arguments you pass to your ruby script
+
+# Line 1 "unpacks" ARGV so that, rather than holding all the arguments
+# it gets assigned to three variables you can work with first, second and third
+# The name of the script itself is stored in a special variable
+# $0 which we dont need to unpack.
+# This may look strange, but "unpack" is probally the best word to describe
+# what it does, it just says "Take whatever is in ARGV, unpack it and
+# assign it to all of these variables on the left in order."
+
+
+ first, second, third = ARGV
+ puts "The script is called: #{$0}"
+ puts "Your first variable is: #{first}"
+ puts "Your second variable is: #{second}"
+ puts "Your third variable is: #{third}"
+

ex13_parameters2.rb

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+first, second, third = ARGV
+
+puts "The script is called: #{$0}"
+print "We are using gets.chomp. to get variables"
+
+var  = STDIN.gets.chomp()
+puts
+puts "Your first variable is: #{first}"
+puts "Your second variable is: #{second}"
+puts "Your third variable is: #{third}"

ex13_parameters2.rb~

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+# Exercise 13-b: Parameters, Unpacking, Variables
+
+first, second, third = ARGV
+
+puts "The script is called: #{$0}"
+print "We are using gets.chomp. to get variables"
+
+var  = STDIN.gets.chomp()
+puts
+puts "Your first variable is: #{first}"
+puts "Your second variable is: #{second}"
+puts "Your third variable is: #{third}"

ex14_prompt.rb

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+
+user = ARGV.first
+prompt = '> '
+
+puts "Hi #{user}, I'm the #{$0} script."
+puts "I'd like to ask you a few questions."
+puts "Do you like me #{user}?"
+print prompt
+likes = STDIN.gets.chomp()
+
+puts "Where do you live #{user}?"
+print prompt
+lives = STDIN.gets.chomp()
+
+puts "What kind of computer do you have?"
+print prompt
+computer =  STDIN.gets.chomp()
+
+puts <<MESSAGE
+Alright, so you said #{likes} about liking me.
+You live in #{lives}. Not sure where that is.
+And you have a #{computer} computer. Nice.
+MESSAGE

ex14_prompt.rb~

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+# Exercise 14: Prompting And Passing
+
+user = ARGV.first
+prompt = '> '
+
+puts "Hi #{user}, I'm the #{$0} script."
+puts "I'd like to ask you a few questions."
+puts "Do you like me #{user}?"
+print prompt
+likes = STDIN.gets.chomp()
+
+puts "Where do you live #{user}?"
+print prompt
+lives = STDIN.gets.chomp()
+
+puts "What kind of computer do you have?"
+print prompt
+computer =  STDIN.gets.chomp()
+
+puts <<MESSAGE
+Alright, so you said #{likes} about liking me.
+You live in #{lives}. Not sure where that is.
+And you have a #{computer} computer. Nice.
+MESSAGE

ex15_readingfiles.txt

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+# exercise 15: reading files
+# ruby.learncodethehardway.org
+
+filename = ARGV.first
+
+prompt = "> "
+txt = File.open(filename)
+
+puts "Here's your file: #{filename}"
+puts txt.read()
+
+puts  "I'll also ask you to type it again:"
+print prompt
+file_again = STDIN.gets.chomp()
+
+txt_again = File.open(file_again)
+
+puts txt_again.read()

ex15_sample.txt

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+This is stuff I typed into a file.
+It is really cool stuff.
+Lots and lots of fun to have in here. 

ex16_readingwriting.rb

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+
+filename = ARGV.first
+raise RuntimeError.new "No input file" unless ARGV.count > 0
+
+script = $0
+
+puts "We're going to erase #{filename}."
+puts "If you don't want that, hit CTRL-C (^C)."
+puts "If you do want that, hit RETURN."
+
+print "? "
+STDIN.gets
+
+puts "Opening the file..."
+target = File.open(filename,'w')
+
+puts "Truncating the file. Goodbye!"
+target.truncate(target.size)
+
+puts "Now I'm going to ask you for three lines."
+
+print "Line 1: "; line1 = STDIN.gets.chomp()
+print "Line 2: "; line2 = STDIN.gets.chomp()
+print "Line 3: "; line3 = STDIN.gets.chomp()
+
+puts "I'm going to write these to the file."
+
+target.write(line1)
+target.write("\n")
+target.write(line2)
+target.write("\n")
+target.write(line3)
+target.write("\n")
+
+puts "And finally, we close it."
+target.close()

ex16_readingwriting.rb~

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+# exercise 16, reading and writing files
+
+filename = ARGV.first
+raise RuntimeError.new "No input file" unless ARGV.count > 0
+
+script = $0
+
+puts "We're going to erase #{filename}."
+puts "If you don't want that, hit CTRL-C (^C)."
+puts "If you do want that, hit RETURN."
+
+print "? "
+STDIN.gets
+
+puts "Opening the file..."
+target = File.open(filename,'w')
+
+puts "Truncating the file. Goodbye!"
+target.truncate(target.size)
+
+puts "Now I'm going to ask you for three lines."
+
+print "Line 1: "; line1 = STDIN.gets.chomp()
+print "Line 2: "; line2 = STDIN.gets.chomp()
+print "Line 3: "; line3 = STDIN.gets.chomp()
+
+puts "I'm going to write these to the file."
+
+target.write(line1)
+target.write("\n")
+target.write(line2)
+target.write("\n")
+target.write(line3)
+target.write("\n")
+
+puts "And finally, we close it."
+target.close()

ex17_morefiles.rb

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+
+from_file, to_file = ARGV
+script = $0
+puts "Copying from #{from_file} to #{to_file}"
+# we could do these two on one line too, how?
+input = File.open(from_file)
+indata = input.read()
+puts "The input file is #{indata.length} bytes long"
+puts "Does the output file exist? #{File.exists? to_file}"
+puts "Ready, hit RETURN to continue, CTRL-C to abort."
+STDIN.gets
+output = File.open(to_file, 'w')
+output.write(indata)
+puts "Alright, all done."
+output.close()
+input.close()

ex17_morefiles.rb~

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+# Exercise 17. More Files
+
+from_file, to_file = ARGV
+script = $0
+puts "Copying from #{from_file} to #{to_file}"
+# we could do these two on one line too, how?
+input = File.open(from_file)
+indata = input.read()
+puts "The input file is #{indata.length} bytes long"
+puts "Does the output file exist? #{File.exists? to_file}"
+puts "Ready, hit RETURN to continue, CTRL-C to abort."
+STDIN.gets
+output = File.open(to_file, 'w')
+output.write(indata)
+puts "Alright, all done."
+output.close()
+input.close()

ex2.rb

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+# Anything after the # is ignored by Ruby
+
+puts "I could have code like this." # and the comment after is ignored
+
+# You can also use a comment to "disable" or comment out a piece of code:
+# puts "This won't run."
+
+puts "This will run." 

ex2.rb~

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+# A comment, this is so you can read you program later.
+# Anything after the # is ignored by Ruby
+
+puts "I could have code like this." # and the comment after is ignored
+
+# You can also use a comment to "disable" or comment out a piece of code:
+# puts "This won't run."
+
+puts "This will run."