Ruby Tutorial with Code Samples

Last updated March 03, 2018

Ruby for the Attention Deficit Disorder Programmer - let's start learning Ruby fast!

"Java is a pair of scissors, Ruby is a chainsaw." -Mitch Fincher

Install Ruby
You can download Ruby from https://www.ruby-lang.org/en/downloads/
Our first program
Enter the following into the file, "test.rb".
```
 
puts "Howdy!"
```
At the C: prompt enter,
```
 
C:>ruby test.rb
```
This produces:
```
 
Howdy!
```
OK, daylight's burning, let's move on.

Output in Ruby

"puts" writes to the screen with a carriage return at the end.
"print" does the same thing without the carriage return.
"printf" formats variables like in C and Java.

 
puts "puts works"
puts " with line breaks."

print "print works"
print " with no line breaks."

printf("\n\nprintf formats numbers like %7.2f, and
strings like %s.",3.14156,"me")

This produces:

puts works
 with line breaks.
print works with no line breaks.

printf formats numbers like    3.14, and strings like
me.

Reading from the Console

Use "gets"

puts "What is your name?"
$name = STDIN.gets
puts "Hi "+$name

Functions

Our first Ruby function

'def' starts the definition of a method, and 'end' ends it - no cute little curly braces.

def welcome(name)
   puts "howdy #{name}"   # inside double quotes, #{ } will evaluate the variable
end
welcome("nana")           # traditional parens

This Produces:

howdy nana

Parentheses are optional

def welcome(name)
   puts "howdy #{name}"   # inside double quotes, #{ } will evaluate the variable
end
welcome "visitor"         #look, ma, no parentheses

This Produces:

howdy visitor

The same is true of methods without arguments

"hello".upcase() => "HELLO"
"hello".upcase => "HELLO"

How to return values from a function
We can use the faithful 'return'
```
def multiply(a,b)
  product = a * b
  return product
end
puts multiply(2,3)   =>6
```
Oddly enough you can leave out the "return" statement, and Ruby will helpfully return the last expression:
```
def mult(a,b)
  product = a * b
end
puts mult(2,3)
```
or even simpler, leave out "product" and ruby returns the contents of the last expression:
```
def mult(a,b)
   a * b
end
puts mult(3,3)   =>9
```

Optional argument values

Ruby lets you assign values to arguments which may, or may not be supplied as shown below:

def test(a=1,b=2,c=a+b)
  puts "#{a},#{b},#{c}"
end
test        =>  1,2,3
test 5      =>  5,2,7
test 4, 6   =>  4,6,10
test 3, 4, 6   =>  3,4,6

Extra arguments

Extra arguments are gathered into the last variable if preceded with a "*". ("each" is an iterator that loops over its members).

def test(a=1,b=2,*c)
  puts "#{a},#{b}"
  c.each{|x| print " #{x}, "}  # We will learn about "each" very soon.  I promise.
end
test 3, 6, 9, 12, 15, 18

This produces:

3,6
 9,  12,  15,  18,

Multiple return values

def getCostAndMpg
    cost = 30000  # some fancy db calls go here
    mpg = 30
    return cost,mpg
end
AltimaCost, AltimaMpg = getCostAndMpg
puts "AltimaCost = #{AltimaCost}, AltimaMpg = #{AltimaMpg}"

Produces:

AltimaCost = 30000, AltimaMpg = 30

Open Classes
You can add methods to existing library classes. For example, in C# 2.0, Microsoft added the very helpful string function, IsNullOrEmpty() which replaces the unwieldly construct:
if(mystring != null && mystring != "")
In Ruby you don't have to wait for the mavens in Redmond to decide you need a new string function, you can add it yourself.
```
class String
    def NullOrEmpty?
    (self == nil || self == "")
    end
end
puts "test".NullOrEmpty?
puts "".NullOrEmpty?
```
Is this way cool? Yes. Is this very dangerous? Yes. Remember, Ruby is a chainsaw.
Variable naming
Ok, let's slow down and learn some basics about variable names
1. Global variables start with '$'
2. Class variables start with '@@'
3. Instance variables start with '@'
4. Local variables, method names, and method parameters start with a lower case letter
5. Class names, module names and constants start with an uppercase letter
6. Variables names are composed of letters, numbers and underscores
7. Method names may end with "?", "!", or "=". Methods ending with a "?" imply a boolean operation (eg, "instance_of?"). Methods ending with "!" imply something dangerous, like strings being modified in place (eg, "upcase!")
Interesting tidbits about Ruby,
1. '#' is the line comment character, all characters after this are ignored. Confusingly '#' can appear within quotes with a different meaning.
2. No semi-colons are needed to end lines, but may be used to separate statements on the same line
3. A backslash (\) at the end of a line is used for continuation
4. Indenting is not significant, unlike python
5. Types of variables do not need to be declared
6. Lines between =begin and =end are ignored
7. Lines following "__END__" on its own line with no white space, are ignored
8. A tiny demonstration of these:
```
# sample program showing special characters like comments
# I'm a comment line
a = 1  #notice no semicolon and no type declaration
b = 2; c = 3 #notice two statements on one line
name = "Abraham \
Lincoln"   # a line continued by trailing \
puts "#{name}"
=begin
I'm ignored.
So am I.
=end
puts "goodbye"
__END__
1
2
3
4
```
```
Abraham Lincoln
goodbye
```
Variable Types
In Ruby, variables don't have a specific type associated with them. All variables are objects, so we only play with pointers to those objects, and those pointers are type agnostic.
```
bat = "Louisville slugger"
bat = 1.23
```
Quotes
Like in Perl, single quotes and double quotes have different meanings.

Double quotes means "please interpret special characters in this string". Things like backslash n ('\n') are converted to their typical values. The #{name} construct is converted to its value.

With single quotes, no special characters are interpreted.

Examples:
```
name="Mike"
puts "hi #{name}" =>hi Mike
puts "hi\n #{name}" => hi (carriage return)Mike
puts 'hi\n #{name}' => hi\n #{name}    (no substitutions are made since using single quote)
```
The braces are optional for global and instance variables
```
$myname="Ishmael"
puts "hi #$myname" =>hi Ishmael
```
Objects
A great thing about Ruby is that numbers and strings are real objects.
```
1.5.floor()   => "1" 
```
This lets us do some cool things. Instead of
```
if( x > 7 && x < 12 ) { ... }
```
We can write
```
if x.between?(7,12) do ...
```

Big Numbers

Ruby automatically increases the precision of variables

for i in 1..1000
  puts "2 ** #{i} = #{2**i}"
end

Produces:

2 ** 1 = 2
2 ** 2 = 4
2 ** 3 = 8
2 ** 4 = 16
2 ** 5 = 32
2 ** 6 = 64
2 ** 7 = 128
2 ** 8 = 256
2 ** 9 = 512
2 ** 10 = 1024
...
2 ** 1000 = 107150860718626732094842504906000181056140481170553360744375038837035105112493612249319837881569585812759467291755314682518714528569231404
359845775746985748039345677748242309854210746050623711418779541821530464749835819412673987675591655439460770629145711964776865421676604298316526243868
37205668069376

Ruby will increase the precision of the number, or decrease it as needed:

x = 1000000
puts "#{x}  "+x.class.to_s    => 1000000  Fixnum
x = x * x
puts "#{x}  "+x.class.to_s    => 1000000000000  Bignum
x = x / 1000000
puts "#{x}  "+x.class.to_s    => 1000000  Fixnum

Parallel Assignment
You can swap the values in variables without the use of a temp variable. Remember your first programming class: Swap the values in "i" and "j"? You had to use a "t" variable to store one of the values first. Not needed in Ruby.
```
i = 0
j = 1
puts "i = #{i}, j=#{j}"
i,j = j,i
puts "i = #{i}, j=#{j}"
```
Produces:
```
i = 0, j=1
i = 1, j=0
```

Collections

Arrays

An array of known objects can be created by enclosing them in square brackets.
```
nums = [1, 2.0, "three"]
puts nums[2]  => three
```
Ruby arrays, like all right-thinking collections, are zero based.
You can use negative indexes to start from the end of the array
```
nums = [1, 2.0, "three", "four"]
puts nums[-1]   => four
```
Using "-1" is so much more concise than "nums[nums.length()-1]".
You can even use the handy "first" and "last" methods.
```
[1,2,3].last  => 3
[1,2,3].first => 1
```

length

To get the count, or size, of an array, use the "length" method.

mystuff = ["tivo","nokia", "ipaq"]  # make a string array
puts mystuff.length  => 3

%w shortcut
Since many arrays are composed of single words and all those commas and quote marks are troublesome, Ruby provides a handy shortcut, %w:
```
mystuff = %w{tivo nokia ipaq}  # make a string array
```
inspect
To look at contents of an object use the "inspect" method. Even more convenient is to use "p" as a shorthand for "puts obj.inspect"
```
myarray = [1,2,5,7,11]
puts myarray
puts myarray.inspect
p myarray
```
Produces:
```
1
2
5
7
11
[1, 2, 5, 7, 11]
[1, 2, 5, 7, 11]
```

Arrays can act like queues and sets

# & is the intersection operator 
puts [1,2,3] & [3,4,5]  #  prints 3

# + is the addition operator 
puts [1,2,3]+ [3,4,5]  #  prints 1,2,3,3,4,5

# - removes items from the first array that appear in the second
puts [1,2,3] - [3,4,5]  #  prints 1,2

# pop returns the last element and removes it from the array
alpha = ["a","b","c","d","e","f"]
puts "pop="+alpha.pop   # pop=f
puts alpha.inspect      # ["a", "b", "c", "d", "e"]

# push appends elements to the end of an array
alpha = ["a","b","c"]
alpha.push("x","y","z")
puts alpha.inspect      # ["a", "b", "c", "x", "y", "z"]

# shift returns the first element and removes it from the array
alpha = ["a","b","c","d","e","f"]
puts "shift="+alpha.shift   # shift=a
puts alpha.inspect      # ["b", "c", "d", "e", "f"]

# unshift appends elements to the beginning of an array
alpha = ["a","b","c"]
alpha.unshift("x","y","z")
puts alpha.inspect      # ["x", "y", "z", "a", "b", "c"]

Hashes

This type of collection is also called a dictionary or an associative array.

Simple hash of cars and their makers

cars = {
'altima' => 'nissan',
'camry' => 'toyota',
'rx7' => 'mazda'
}
puts cars['rx7']   =>   mazda

You can create a hash and fill it dynamically

dict = {}  # create a new dictionary
dict['H'] = 'Hydrogen' #associate the key 'H' to the value 'Hydrogen'
dict['He'] = 'Helium'
dict['Li'] = 'Lithium'
p dict['H']       # prints "Hydrogen"
p dict.length     # prints 3
p dict.values     # prints ["Lithium", "Helium", "Hydrogen"]
p dict.keys       # prints ["Li", "He", "H"]
p dict            # prints {"Li"=>"Lithium", "He"=>"Helium", "H"=>"Hydrogen"}

Hash[]

You can also create Hashes with square brackets by prefixing with "Hash":

toppings = Hash["pancakes","syrup","Pizza","Pepper","Cereal","Sugar"]
puts toppings.inspect

Produces:

{"Pizza"=>"Pepper", "Cereal"=>"Sugar", "pancakes"=>"syrup"}

each

The "each" method is a wonderful way to iterate over the keys

toppings = Hash["pancakes","syrup","Pizza","Pepper","Cereal","Sugar"]
toppings.each{|key, value| puts "#{key} points to #{value}"}

Produces:

Pizza points to Pepper
Cereal points to Sugar
pancakes points to syrup

select

The "select" method populates a new array with members which meet a criteria

salaries = Hash["bob",10.9,"larry",7.5,"jimmy",6.0,"jerry",6.5]
salaries.inspect
mySalaryArray = salaries.select{|name,salary| salary > 7.0}
puts mySalaryArray.inspect #prints  [["larry", 7.5], ["bob", 10.9]]

Ranges
Ranges are composed of expr..expr or expr...expr. Two dots includes the last element, three dots excludes it.
```
('a'..'g').each{ |letter| puts letter }
```
Produces:
```
a
b
c
d
e
f
g
```
```
(1...3).each{ |num| puts num }
```
Produces only two numbers since "..." does not include the last element.:
```
1
2
```

Control Statements

if In an "if" statement anything but the two special values, "false" and "nil" are considered true. Even zero is true for all you C/C++ programmers.
```
income = 30000.00
if income < 10000
  rate = 0.02
elsif income < 30000
  rate = 0.28
else
  rate = 0.5
end
puts rate
```

case

grade = 10
school = case grade
when 0..5
   "elementary"
when 6..8
   "middle school"
when 9..12
   "high school"
else
   "college"
end
puts "grade #{grade} is in #{school}"

for

for i in 1..4 
 puts "hi #{i}"
end

The ranges can of course have variables

top = 6
for i in 1..top
 puts "hi #{i}"
end

exit

lines = IO.readlines("data.txt")
if lines.length < 100
   exit 2
end
puts lines.length

loop

iterates over code until a "break" or eternity ends

i=0
loop do
   break if i > 5
   puts i
   i += 1  
end

Statement modifiers
These are just syntatic sugar.
1. if
  The "if" clause may be placed at the end of a statement
```
balance = -10.0
puts "Bankrupt" if balance < 0.0
```
2. unless
  "unless" is placed at the end of a statement
```
balance = -10.0
puts "Bankrupt" unless balance > 0.0
```
3. while
  "while" may be after its block
```
f=2
puts f=f+2 while f < 10
=>4
=>6
=>8
=>10
```

Iterators

while

i = 0
while i  < 5
  i = i+1
  puts i
end

"times"

n = 10
n.times { |i| print i}

Produces:

0123456789

"each"

animals = %w(lions tigers bears)
animals.each{|kind| print kind}

lionstigersbears

"each" with ranges

('m'..'z').each {|ch| print ch}

mnopqrstuvwxyz

"upto"

n=0 ; max=7
n.upto(max) {|num| print num}

01234567

You gotta have class.

Classes
Class definitions start with "class" and end with "end". Remember that class names start with a capital letter. Notice the syntax is "object.new" for creating an object and that the "initialize" method contains code normally found in the constructor. Here's a small example:
```
class Person
  def initialize(fname, lname)
   @fname = fname
   @lname = lname
  end
end
person = Person.new("Augustus","Bondi")
print person
```
Produces:
```
#<Person:0x257c020>
```
which is true, but not helpful.

The "ToString" method, to_s

class Person
  def initialize(fname, lname)
   @fname = fname
   @lname = lname
  end
  def to_s
     "Person: #@fname #@lname"
  end
end
person = Person.new("Augustus","Bondi")
print person

Produces:

Person: Augustus Bondi

Subclassing
In Ruby subclassing is done with the "<" character
```
class Employee < Person
  def initialize(fname, lname, position)
    super(fname,lname)
    @position = position
  end
  def to_s
     super + ", #@position"
  end
end
employee = Employee.new("Augustus","Bondi","CFO")
print employee
```
Produces:
```
Person: Augustus Bondi, CFO
```
if we try to print the first name directly like
```
print employee.fname
```
we get the error message,
```
CFOtest.rb:21: undefined method 'fname'
```
But why is that? We've printed variables a zillion times up til now and it's always worked. What changed? Up until now we've created variables in a program without classes (actually all are variables were members of a default object that were accessable inside itself). Now we are using real classes and that brings up the point of visibility of members outside the class. We now have to specify if a variable is open to the outside, like "public", "private", "protected", "internal" in other languages.

To grant access to read a variable we declare it after "attr_reader". attribute with the following:
```
  attr_reader :fname, :lname
```
then
```
print employee.fname  =>   "Augustus"
```
To allow writing to a variable use "attr_writer",
```
class Employee < Person
  def initialize(fname, lname, position)
    super(fname,lname)
    @position = position
  end
  def to_s
     super + ", #@position"
  end
  attr_writer :position
end
employee = Employee.new("Augustus","Bondi","CFO")
puts employee
puts employee.fname
employee.position = "CEO"
puts employee
```

Virtual Attributes

class Employee < Person
  def initialize(fname, lname, position)
    super(fname,lname)
    @position = position
  end
  def to_s
     super + ", #@position"
  end
  attr_writer :position
  def etype
     if @position == "CEO" || @position == "CFO"
         "executive"
     else
         "staff"
     end
  end
end
employee = Employee.new("Augustus","Bondi","CFO")
employee.position = "CEO"
puts employee.etype    =>  executive
employee.position = "Engineer"
puts employee.etype    =>  staff

Regular Expressions

Strings can be compared to a regular expression with "=~". Regular expressions are surrounded by "//" or "%r{}". Anything but the two special values, "false" and "nil" are considered true.

Expression	Result	Description

/a/ =~ "All Gaul is divided into three parts"	5	finds the first "a" at position 5
%r{a} =~ "All Gaul is divided into three parts"	5	same thing with alternate syntax
/ree/ =~ "All Gaul is divided into three parts"	27	finds "ree" at position 27
/^a/ =~ "All Gaul is divided into three parts"	nil	"^" implies at the beginning of a line. nil is false.
/^A/ =~ "All Gaul is divided into three parts"	0	case-sensitive, remember that "0" is true
/s$/ =~ "All Gaul is divided into three parts"	35	"$" implies at the end of a line
/p.r/ =~ "All Gaul is divided into three parts"	31	"." matches any character

Blocks

And now to one of the coolest things about Ruby - blocks. Blocks are nameless chunks of code that may be passed as an argument to a function.

Simple Example
```
def whereisit
   yield
   yield
   yield
end
whereisit {puts "where is the money?"}
```
Produces:
```
where is the money?
where is the money?
where is the money?
```
In the above example '{puts "where is the money?"}' is called a block. That chunk of code is passed to the method "whereisit" and executed each time the "yield" statement is executed. You can think of the "yield" being replaced by the block of code.

Blocks can take arguments

Here the method "cubes" takes the max value.

def cubes(max)
   i=1
   while i < max
      yield i**3
      i += 1
   end
end
cubes(8) { |x| print x, ", "}   => 1, 8, 27, 64, 125, 216, 343,
sum = 0
cubes(8) { |y| sum += y}
print "\nsum=",sum              => sum=784
product = 1
cubes(8) { |z| product *= z}
print "\nproduct=",product      => product=128024064000

Think of the "yield i**3" in the function cubes as being replaced with the block, '|x| print x, ", "'. The value following the "yield" is passed as the value "x" to the block.

Multiple arguments may be passed to blocks.

def employee(empId)
      #next 2 lines simulated from calling a database on the empId
      lastname = "Croton"
      firstname = "Milo" 
      yield lastname,firstname  #multiple arguments sent to block
end
employee(4) { |last,first| print "employee ",": ",first, " ",last}

Produces:

employee : Milo Croton

Local variables can be shared with a block

Even though rate is a local variable, it is used inside the block.

def tip(mealCost) 
   yield mealCost
end
rate = 0.15
mytip = tip(10.0) { |cost| cost * rate }
print "tip should be: ",mytip

Produces:

tip should be: 1.5

Blocks are built in to many objects in ruby

each
iterates through each item of a collection
```
[1,2,3,4].each{|x| print x**2," "}
```
Produces:
```
1 4 9 16
```

detect

returns the first item matching a logical expression

numbers = [1,3,5,8,10,14]
firstDoubleDigit = numbers.detect {|x| x > 9}
print firstDoubleDigit  => 10

select

returns all items matching a logical expression

numbers = [1,2,3,4,5,6,7];
evens = numbers.select{|x| x % 2 == 0}
p evens =>   [2, 4, 6]

collect

returns an array created by doing the operation on each element.

[1,2,3,4].collect{|x| x**3}   => [1, 8, 27, 64]
["the","quick","brown", "lox"].collect{|x| x.upcase} => ["THE", "QUICK", "BROWN", "LOX"]

inject

"inject" is the "fold" or "reducer" function in Ruby. "inject" loops over an enumerable and performs an operation on each object and returns a single value.

primes = [1,3,5,7,11,13];
#using "inject" to sum.  We pass in "0" as the initial value
sum = primes.inject(0){|cummulative,prime| cummulative+prime}
puts sum    =>40
#we pass in no initial value, so inject uses the first element
product = primes.inject{|cummulative,prime| cummulative*prime}
puts product    =>15015
#just for fun let's sum all the numbers from 1 to, oh, say a million
sum = (1..1000000).inject(0){|cummulative,n| cummulative+n}
puts sum   =>500000500000
#you can do interesting things like build hashes
hash = primes.inject({}) { |s,e| s.merge( { e.to_s => e } ) }
p hash  #   =>  {"11"=>11, "7"=>7, "13"=>13, "1"=>1, "3"=>3, "5"=>5}

File I/O

Read an entire file into a string

file = File.new( "t1.php" )
mytext = file.read

Read an entire file into an array of lines

lines = IO.readlines("data.txt")
puts lines[0]  #prints the first line

Read a file line by line

file = File.open("res.txt")
   while line = file.gets
      puts line
   end

Or you can use the IO class

IO.foreach("data.txt") { |line| puts line }

Read a file line by line

You should ensure the file is closed as well.

begin
file = File.open("res.txt")
   while line = file.gets
      puts line
   end
ensure
   file.close
end

Read only a few bytes at a time
The following snippet of code reads a file which may have no line breaks and chops it into 80 character lines
```
require 'readbytes'
file = File.new( "C:/installs/myapp_log.xml" )
while bytes = file.readbytes(80) 
   print bytes+"\r\n"
end
file.close
```

Reads a large XML file and inserts line breaks

Uses TruncatedDataError to grab the last few slacker bytes from the end.

# reads an xml file without line breaks and puts a line break before each '<'
require 'readbytes'
file = File.new( "C:/installs/MyProject_log.xml" )
begin
   while bytes = file.readbytes(80) 
      print bytes.gsub(/</,"\r\n<")
   end
rescue TruncatedDataError #the last read had less chars than specified
   #print the rest of the data.  $! is the exception.
   # ".data" has the extra bytes
   print $!.data.gsub(/</,"\r\n<") 
ensure
   file.close unless file.nil?
end

method_missing - a wonderful idea
In most languages when a method cannot be found and error is thrown and your program stops. In ruby you can actually catch those errors and perhaps do something intelligent with the situation. A trivial example:
```
class MathWiz
  def add(a,b) 
    return a+b
  end
  def method_missing(name, *args)
    puts "I do not know the method #{name}"
  end
end
mathwiz = MathWiz.new
puts mathwiz.add(1,4)
puts mathwiz.subtract(4,2)
```
Produces:
```
5
I don't know the method subtract
nil
```
While the ruby program is loading, you can execute code inside a special block labeled "BEGIN" - pretty nifty. After the interpretor has loaded the code, but before execution, you can execute code in the "END" block.
```
puts "main program running"
END {
puts "program ending"
}
BEGIN {
puts "I am loading"
}
```
Produces:
```
I am loading
main program running
program ending
```
converting between strings and ints
Use the to_i and to_s methods
```
"3".to_i  #return an integer
3.to_s    # returns a string
```

Using XML Dom Parser

REXML goes standard with Ruby 1.8. Sample to print all "div" elements whose "class" attribute is set to "entry".

require "rexml/document"
file = File.new( "t0.xml" )
doc = REXML::Document.new file
doc.elements.each("//div[@class='entry']") { |element| puts element }

Run a few lines directly from the command line with the "-e" option

c:\home\mfincher>ruby -e 'sleep 2'
c:\home\mfincher>ruby -e 'puts 3*4'
12
c:\home\mfincher>ruby -e 'puts 3*4; puts 4*4'
12
16

Editing files in place

Ruby offers a simple way to make a string substitution in many files all at once with a single line of code. The "-p" option loops over the files, the "-i" is the backup extension. With this command we are changing all the documentation from version 1.5 to 1.6, but the original files are renamed to ".bak".

C:\home\mfincher\ruby>more v2.txt
Regarding version 1.5 ...
....
version 1.5 is easy to install

C:\home\mfincher\ruby>ruby -pi.bak -e "gsub(/1.5/,'1.6')" v*.txt

C:\home\mfincher\ruby>more v2.txt
Regarding version 1.6 ...
....
version 1.6 is easy to install

C:\home\mfincher\ruby>more v2.txt.bak
Regarding version 1.5 ...
....
version 1.5 is easy to install

Example of printing duplicate lines in sorted file.

#prints duplicate lines in sorted files in the file passed in as first arg
file = File.open(ARGV[0])
lastLine = ""
counter = 0
   while line = file.gets
        counter += 1
	if lastLine == line 
           puts "#{counter-1}: #{line}#{counter}: #{line}\r\n"
        end
	lastLine = line	
   end
puts "done. Processed #{counter} lines"

Ruby has its own interpreted shell, irb.

C:\home\mfincher>irb
irb(main):001:0> puts "Hello World"
Hello World
=> nil
irb(main):002:0> a=1
=> 1
irb(main):003:0> a*2
=> 2
irb(main):004:0>

ruby can take input from stdin
```
echo 'puts "hello"' | ruby
```
to pass a string on the url it needs to be "escape"'d first.
```
require 'uri'
...
URI.escape("some string...")
```

Example to remove "funny" characters from a filename

Example of iterating over the filenames in a directory, using regular expression substitution in strings, and renaming files.

#replaces any "funny" characters in a filename in the current directory with an underscore
#if the new file name already exists, this skips it.
Dir.foreach(".") { |f| 
  print "testing \"#{f}\""
  if f =~ /[^\w\-\.]/   #filename contains something other than letters, numbers, _,-, or .
     puts "\r\n   name with funny characters: #{f}"
     newName = f.gsub(/[^\w\.\-]/,"_")   # \w is any word character, letter,num or _
     if File.exist?(newName)
	puts "   File #{newName} already exists.  Not renaming."
     else
	puts "   renaming #{f} to #{newName}"
	File.rename(f,newName)
     end
  else
    puts "   it's ok."
  end
}

Looping over list of arguments

ARGV.each {|f|
puts f
counter = 0
file = File.open(f,"r")
   ftmp = f+".tmp"
   tmp = File.open(ftmp,"w")
   while line = file.gets
   if line =~ /pid="2"/
     counter += 1
     line = line.gsub(/pid="2"/,"pid=\"#{f}:#{counter}\"")
     puts line
   end
   tmp.print line
end
file.close
tmp.close
puts "renaming #{ftmp} to #{f}"
File.rename(ftmp,f)
}

Miscellanous Commands

command	description	example	result
global_variables	returns all global variables
local_variables	returns all local variables
sleep seconds	sleeps specified seconds
rand	returns a random number between 0 and 1
rand(max)	returns int between 0 and max
warn	like print, but writes to STDERR

Interesting string functions

command	description	example	result
center	centers string	"City".center(20)	"________City________"
ljust	left justifies	"State".ljust(30)	"State_________________________"
rjust	right justifies	"State".rjust(30)	"_________________________State"
include?	does the string include this substring	"this is a test".include?('is')	true
gsub	global regex replacesments	"this is a test".gsub(/[aeiou]/,'_\1')	th_s _s _ t_st
tr	translates	"The greatest of these is".tr('aeiou','*')	Th* gr*tst f ths* *s
each	splits and iterates	"one:two:three".each(':'){\|x\| puts x}	one: two: three

DateTime

puts DateTime.now  #prints 2006-11-25T14:26:15-0600
puts Date.today    #prints 2006-11-25
puts Time.now      #prints Sat Nov 25 14:29:57 Central Standard Time 2006

Using 'require'
require will let your access code from other files. 'require' looks in directories specified in $LOAD_PATH to find the files. The environmental variable RUBYLIB can be used to load paths into $LOAD_PATH.
```
C:\home\mfincher\ruby>irb
irb(main):001:0> p $LOAD_PATH
["c:/opt/ruby/lib/ruby/site_ruby/1.8", "c:/opt/ruby/lib/ruby/site_ruby/1.8/i386-msvcrt", "c:/opt/ruby/lib/ruby/site_ruby", "c:/opt/ruby/lib/ruby/1.8",
 "c:/opt/ruby/lib/ruby/1.8/i386-mswin32", "."]
=> nil
```
You can put a library like 'startClicker.rb' in any of those directories and ruby will find it.
```
require 'startClicker'
```
BuiltIn Command Interpreter
With the "eval" method you can create your own interpreter language and run it during execution.
```
irb(main):007:0> a = 6
=> 6
irb(main):008:0> b = 7
=> 7
irb(main):009:0> eval "c=a+b"
=> 13
irb(main):010:0> puts c
13
```

Introspection with ObjectSpace

You can find all the objects in your program of a particular type using ObjectSpace.each_object.

class Person
  def initialize(name,age)
    @name = name
    @age = age
  end
  attr_reader :name
end
p = Person.new("Alfred",34)
p2 = Person.new("Janie",31)
ObjectSpace.each_object(Person) {|s| 
   puts s.name 
}

Produces:

Janie
Alfred

Testing

Ruby comes right out of the box with a testing framework. Here's a quick example:

require 'test/unit'

class TestMe < Test::Unit::TestCase

  def test_add
    s = 1 + 1
    assert_equal(2, s)
  end

end

Read a URL and print the web page to the screen.

This will get a particular page and print to the screen:

require 'open-uri'
open('http://www.fincher.org/Misc/Pennies'){ |f| print f.read }

This will read a file of urls and print all to the screen:

#Reads first argument as file containing urls and prints them
#usage:  ruby wget.rb wget.txt
require 'open-uri'
IO.foreach(ARGV[0]) { |line| open(line){ |f| print f.read } }

Example of drawing a line on a canvas in Tk

Tk is a graphical subsystem used in languages like Perl and Tcl.

#draws a single line on a big canvas
require 'tk'
include Math

TkRoot.new do |root|
   title "Solo Line"
   geometry "600x600"
   canvas2 = TkCanvas.new(root) do |canvas|
      width 600
      height 600
      pack('side' => 'top', 'fill'=>'both', 'expand'=>'yes')
      points = []
   end
   TkcLine.new(canvas2, 0,0,100,100)
end
Tk.mainloop

irb - interactive ruby

Ruby comes with an REPL (Read Eval Print Loop) utility to let you try ruby interactively. ("inf-ruby.el" provides an internal shell in emacs for irb).

C:>irb
irb(main):001:0> puts "hello"
puts "hello"
hello
nil
irb(main):002:0> Object.methods
Object.methods
["send", "name", "class_eval", "object_id", "new", "singleton_methods", "__send__", "private_method_defined?", "equal?", "taint", "frozen?", "instance_variable_get", "constants", "kind_of?", "to_a", "instance_eval", "require", "ancestors", "const_missing", "type", "instance_methods", "protected_methods", "extend", "protected_method_defined?", "eql?", "public_class_method", "const_get", "instance_variable_set", "hash", "is_a?", "autoload", "to_s", "class_variables", "class", "tainted?", "private_methods", "public_instance_methods", "instance_method", "untaint", "included_modules", "private_class_method", "const_set", "id", "<", "inspect", "<=>", "==", "method_defined?", ">", "===", "clone", "public_methods", "protected_instance_methods", "require_gem", ">=", "respond_to?", "display", "freeze", "<=", "module_eval", "autoload?", "allocate", "__id__", "=~", "methods", "gem", "method", "public_method_defined?", "superclass", "nil?", "dup", "private_instance_methods", "instance_variables", "include?", "const_defined?", "instance_of?"]
irb(main):003:0>

RubyGems a ruby package installer
You can download RubyGems from http://rubyforge.org. Unzip the files (eg, C:\opt\ruby) then install by entering:
```
C:>cd C:\opt\ruby\rubygems-0.9.0
C:\opt\ruby\rubygems-0.9.0>ruby setup.rb all
```

Ruby on Rails

How to write a log message
You can use logger's methods "warn", "info", "error", and "fatal".
```
    logger.info("request.remote_ip"+request.remote_ip);
```
Field names ending with "_at" are assumed to be datetime fields and are filled in automagically by rails for ActiveRecord objects. The suffix "_on" are assumed to be dates.
Console
to dubug applications it's convenient to use the console script
```
myapp>ruby script/console
```
debug method
You can use the debug() method inside web pages to dump info about an object.
```
<p>Thanks for visiting</p>
<%= debug(@myobject) %>
```
How to Freeze a version
Since your hosting company may upgrade the rails version you need to "freeze" the current version. The following copies all the 1.2.6 libraries from the shared directory to your own private one.
```
rake rails:freeze:edge TAG=rel_1-2-6
```

Active record notes

Find all records meeting a criteria

def self.suitable_jokes(sort_key)
if sort_key == "Newest"
   find(:all,
        :conditions => "suitable  = \"1\"",
        :order => "entry_date DESC"
       )
elsif sort_key == "Worst"
   find(:all,
        :conditions => "suitable  = \"1\"",
        :order => "entry_date ASC"
       )
else
   find(:all,
        :conditions => "suitable  = \"1\"",
        :order => "current_rating DESC"
       )
end
end

The first argument to find can also be ":first" or ":last".

Find the count of records meeting a criteria

def self.waiting_jokes()
  count("suitable  = \"0\"")
end
def self.total()
  count("suitable  = \"1\"")
end

Find the total number of items

count = Joke.count

Find the total number of items meeting a criteria

count = Joke.count(["suitable = \"1\""])

Pagination

The ":limit" and ":offset" options allow easy pagination.

To return the fifth page of items use the following:

find(:all,
        :conditions => "suitable  = \"1\"",
        :order => "current_rating DESC",
	:limit => 10,
	:offset => 40
       )

Use raw SQL and return two values

def getAverageRatingAndCount
    record = Rating.find_by_sql(["select count(*) as count,avg(rating) as average from ratings WHERE joke_id = ?",id]);
    return record[0].average.to_f , record[0].count.to_i
end

The "create" method in ActiveRecord will do "new" and "save" operations simultanously.
```
mydog = Dog.create(
:name => "Fido"
:breed => "Collie"
)
```

Watir

Watir is a GUI testing tool written in Ruby. Here is a script to open Google and search for pictures of kittens.

require "watir"
ie = Watir::IE.new  #create an object to drive the browser
ie.goto "http://www.google.com/"
ie.url == "http://www.google.com/"
ie.link(:text, "Images").flash #flash the item text "Images"
ie.link(:text, "Images").click #click on the link to the images search page
ie.text.include? "The most comprehensive image search on the web" #test to make sure it worked
searchTerm = "kittens" #set a variable to hold our search term
ie.text_field(:name, "q").set(searchTerm) # q is the name of the search field
ie.button(:name, "btnG").click # "btnG" is the name of the google button
if ie.contains_text(searchTerm)
  puts "Test Passed. Found the test string: #{searchTerm}. Actual Results match Expected Results."
else
   puts "Test Failed! Could not find: #{searchTerm}"
end

Selecting a JavaScript popup box

stolen from http://wiki.openqa.org/display/WTR/FAQ

#Watir script to show clicking a JavaScript popup box
require "watir"
require 'watir\contrib\enabled_popup'
require 'startClicker'
require 'net/http'
require 'net/https'

$ie = Watir::IE.new  #create an object to drive the browser
$ie.goto "http://mydomain.com/ListGroups.aspx"
if $ie.contains_text("Log In")
  $ie.text_field(:name, "Login1$UserName").set("fincherm")
  $ie.text_field(:name, "Login1$Password").set("mitch")
  $ie.button(:name, "Login1$LoginButton").click 
end
$ie.link(:text, "Baseline").click 
$ie.link(:text, "MoonManC").click 
def setDdlPriority(priority) 
   ddlPriority = $ie.select_list( :name , /ddlPriority/)
   puts ddlPriority
   ddlPriority.select(priority)
   puts ddlPriority
   $ie.button(:name, "ctl00$btnSave").click_no_wait 
      startClicker( "OK", 4 , "User Input" )
      sleep 1   
end
setDdlPriority("2")
setDdlPriority("9")

startClicker.rb:

#method startClicker from http://wiki.openqa.org/display/WTR/FAQ
def startClicker( button , waitTime= 9, user_input=nil )
  # get a handle if one exists
  hwnd = $ie.enabled_popup(waitTime)  
  if (hwnd)  # yes there is a popup
    w = WinClicker.new
    if ( user_input ) 
      w.setTextValueForFileNameField( hwnd, "#{user_input}" )
    end
    # I put this in to see the text being input it is not necessary to work
    sleep 3         
    # "OK" or whatever the name on the button is
    w.clickWindowsButton_hwnd( hwnd, "#{button}" )
    #
    # this is just cleanup
    w=nil    
  end
end

How to use Watir with NUnit

Here is an example of connecting it to NUnit.

using System;
using System.Diagnostics;
using System.Text.RegularExpressions;
using NUnit.Framework;

namespace MyProject.Test.Watir
{
    /// <summary>
    /// from http://www.hanselman.com/blog/IntegratingRubyAndWatirWithNUnit.aspx
    /// with changes by Liz Buenker
    /// </summary>
    public class WatirAssert
    {
        public static void TestPassed(string rubyFileName, string directoryPath)
        {
            string output = String.Empty;
            using (Process p = new Process())
            {
                p.StartInfo.UseShellExecute = false;
                p.StartInfo.RedirectStandardOutput = true;
                p.StartInfo.FileName = "ruby.exe";
                p.StartInfo.Arguments = rubyFileName + " -b";
                p.StartInfo.WorkingDirectory = directoryPath;
                p.Start();
                output = p.StandardOutput.ReadToEnd();
                p.WaitForExit();
            }
            Console.Write(output);
            Trace.Write(output);
            Regex reg = new Regex(@"(?<tests>\d+) tests, (?<assertions>\d+) assertions, (?<failures>\d+) failures, (?<errors>\d+) errors", RegexOptions.Compiled);
            Match m = reg.Match(output);
            try
            {
                int tests = int.Parse(m.Groups["tests"].Value);
                int assertions = int.Parse(m.Groups["assertions"].Value);
                int failures = int.Parse(m.Groups["failures"].Value);
                int errors = int.Parse(m.Groups["errors"].Value);
                if (tests > 0 && failures > 0)
                {
                    Assert.Fail(String.Format("WatirAssert: Failures {0}", failures));
                }
                else if (errors > 0)
                {
                    Assert.Fail(String.Format("WatirAssert: Errors {0}", errors));
                }
            }
            catch (Exception e)
            {
                Assert.Fail("WatirAssert EXCEPTION: " + e.ToString());
            }
        }
    }
}

The above code would be used by something like this:

using System;
using NUnit.Framework;

namespace MyProject.Test.Watir
{
    [TestFixture]
    public class WatirTest
    {
        private static readonly string testDir = Utilities.Properties.baseDir + "\\Test\\Watir";
        public WatirTest() { }
        [Test]
        public void Sd01Test()
        {
            WatirAssert.TestPassed("sd01_test.rb",testDir);
        }
        [Test]
        public void Sd02Test()
        {
            WatirAssert.TestPassed("sd02_test.rb",testDir);
        }

    }
}

Ruby Quotes:

"Ruby is a language for clever people." -Matz
"Ruby is the perlification of Lisp." -Matz
"Type Declarations are the Maginot line of programming." -Mitch Fincher
"Java is a pair of scissors, Ruby is a chainsaw." -Mitch Fincher, with a pair of scissors you can cut yourself and draw blood but with a chainsaw you can lose a limb in a moment of carelessness."