One way to run ruby code is by putting it in a file with a .rb extension, and
running in the terminal using ruby file.rb.
As a quick demonstration, open a new file, and paste this Ruby code into it:
#!/usr/bin/ruby puts 'Hello world'
When you hit the button in the menu bar, the console will print out Hello world.
IRB, or interactive Ruby, is an interactive environment for Ruby scripting. You can open an IRB session in your Cloud9 terminal to practice Ruby coding.
- In Cloud9, open a terminal window.
- In the terminal, run:
irb
A variable is a named space in memory that stores some data. A variable is identified by its name. A variable exists within a scope, and is deleted by a garbage collector when it is no longer needed.
- In irb, look for a variable named x:
x
- To create a variable in ruby, you assign it an initial value:
x = 1
The "=" in ruby is known as the assignment operator. It is used like:
variable_name = variable_value
The data that is stored in a variable may be one of the following types:
- Boolean
- String
- Integer
- Decimal / Float
- Array
- Hash
The type of data is determined by syntax during assignment. For example:
- Boolean:
x = true
Denoted by either the word true or false without quotes around it.
- String:
x = "This is a string"
Denoted by quotes surrounding the value
- Integer:
x = 1Denoted by a number without a decimal point
- Float:
x = 0.1
Denoted by a number with a decimal point
- Array:
x = ["Item 1", "Item 2", "Item 3"]
Denoted by square brackets, with multiple values inside separated by commas
- Hash:
x = {:name => "variable x", :value => 1}
Denoted by curly braces enclosing comma-separated key-value pairs
Ruby is a dynamically typed language. That means that changing the value of a variable implicitly changes its type, since a variable inherits its data type from its value.
x.is_a? Hash x = 1 x.is_a? Hash
In Ruby, you can do all of the normal mathematical arithmetic on integer and decimal/float variables.
| Operation | Operand | Sample Syntax |
| Addition | + |
x + 2 |
| Subtraction | - |
x - 2 |
| Multiplication | * |
x * 2 |
| Division | / |
x / 2 |
| Modulus | % |
x % 2 |
Parentheses can be used to enclose a group of operations, just like in regular math. So:
x = 1 x - 0 * 2 Yeilds: 1 (x - 0) * 2 Yeilds: 2
The order of operations is the same as in regular math.
You can also combine arithmetic and assignment. These operators perform the given arithmetic operation on the variable, and assign the result of that operation to the new value of the variable, replacing the old value. For example:
| Operand | Initial x | Sample Use | Result x |
+= |
1 | x += 2 |
3 |
-= |
3 | x -= 2 |
1 |
*= |
1 | x *= 2 |
2 |
/= |
2 | x /= 2 |
1 |
%= |
1 | x %= 1 |
0 |
If you want to add some data on to a string, you can use the + for this.
For example, if you want to have a string variable called "formatted_x" that uses the value of the integer variable "x" in it:
formatted_x = "$" + x + ".00"
Note that the string portions to be concatenated are surrounded by quotes, and anything not surrounded by quotes represents a variable or method's value.
Also note that if you change the value of x, this will not update the value of formatted_x, since the value of x was inserted into formatted_x, not the variable itself. If you wanted to auto-update formatted_x every time that x is changed, you would have to use a method... read on to find out how.
You may sometimes want to compare the value of a variable to something else. In Ruby, you can do this using the and, or, and is equal to operators:
| Operation | Operand | Sample Syntax |
| And | && |
x && y |
| Or | || |
x || y |
| Is Equal To | == |
x == y |
An example use of the "And"/"Or" comparisons:
"And" and "Or" are used to compare two boolean variables to each other. Say that you have these variables which describe a fast food order:
sandwich = "cheeseburger"
condiments = ["pickles", "mustard", "ketchup"]
combo = true
size = "medium"
drink_upsize = true
order = {
:sandwich => sandwich,
:condiments => condiments,
:combo => combo,
:size => size,
:drink_upsize => drink_upsize
}
... and you want to know whether this order is a combo with an upsized drink:
combo && drink_upsize
This returns true, but if you set one of those variables equal to false, it does not:
drink_upsize = false combo && drink_upsize
So you can see that the "And" comparison checks whether both of the given values are true, and if not, it returns false.
The "Or" comparison checks to see if either one, or both, of the given values is true, and if not, returns false. So:
combo || drink_upsize
Returns true.
An example use of the "Is Equal to" comparison:
The "Is Equal To" comparison can be used on two values of any type to determine if they equal each other.
combo == true --> true combo == drink_upsize --> false combo == "true" --> false sandwich == "burger" --> false
WARNING: Do not confuse == with =!
###If...Else
Conditional statements are the simplest form of branching in coding. The first condtional is the if...else. It's just used to say: if this codition is true, do one thing, if it's not, do another thing. For example:
if order[:sandwich] == "cheeseburger" puts "You ordered a cheeseburger" end if order[:sandwich] == "cheeseburger" puts "You ordered a cheeseburger!" else puts "You didn't order a cheeseburger." end
- So the structure of the if...else is::
- if conditional statement
- code to run if conditional returns true
- else
- code to run if conditional returns false
end
Notice you always need an "end" after any conditional statement, to let the interpreter know where the code that belongs to your branch ends. If you don't have it, you will get an error.
###If...Elsif
Using elsif (short for "else if", and used only in Ruby) allows you to add
more than one conditional to the same statement as your if or if...else.
For example:
if order[:sandwich] == "cheeseburger" puts "You ordered a cheeseburger!" elsif order[:sandwich] == "burger" puts "You ordered a burger!" end if order[:sandwich] == "cheeseburger" puts "You ordered a cheeseburger!" elsif order[:sandwich] == "burger" puts "You ordered a burger!" else puts "You didn't order a burger at all." end
###Unless
Unless is just the opposite of if. Use it when you want some code to run,
unless this one particular condition is met. For example:
unless order[:combo] == false puts "You get fries and a drink with that sammy!" end unless order[:drink_upsize] puts "You get a" + order[:size] + " fries and drink with that sammy!" end
See if you can write a ruby script in a .rb file that will take an order when it is run.
Rails is the most popular framework for doing web applications with ruby. Getting a simple web app up and running on ruby and rails is relatively quick and easy.
First, fork your rails sample app on GitHub. Go to:
https://github.com/vstem-davenport/sample_app
...and click the "fork" button.
Now you have a copy of the project on your Github account.
Next, go to your Cloud9 dashboard and click on the project name under "Projects On Github" in the left sidebar. Then click the "Clone to Edit" button to clone a copy of the project to your Cloud9 virtual workstation.
Once your project is finished cloning to Cloud9, open the project workspace by clicking the "Start Editing" button.
In your rails sample app's Cloud9 project workspace, open a Terminal window. Run:
curl -L https://get.rvm.io | bash -s stable
Once that command finishes, run the following command to check that RVM is working, and also choose a ruby version to use in this project:
rvm use 1.9.3
In your Cloud9 Terminal, run this command to create a name for the rvm gemset that you'll be using for this project:
rvm use --create 1.9.3@rails_sample_app
Run the bundle install command to install all of the gems in your Gemfile:
bundle install
In your rails sample app's Cloud9 Terminal window, run:
rails s -b $IP -p $PORT
That's it! Your rails app will now be running. You can view your running rails app at https://<workspacename>.<username>.c9.io.
In the terminal:
c9pm install heroku heroku create git add . git status git commit -m "Initial commit." git push git push heroku master
see page 10
https://docs.c9.io/writing_a_ruby_app.html https://github.com/mhartl/sample_app http://ruby.railstutorial.org/ http://guides.rubyonrails.org/ https://devcenter.heroku.com