Keywords
| KEYWORD | DESCRIPTION | EXAMPLE |
|---|---|---|
| BEGIN | Run this block when the script starts. | BEGIN { puts "hi" } |
| END | Run this block when the script is done. | END { puts "hi" } |
| alias | Create another name for a function. | alias X Y |
| and | Logical and, but lower priority than &&. | puts "Hello" and "Goodbye" |
| begin | Start a block, usually for exceptions. | begin end |
| break | Break out of a loop right now. | while true; break; end |
| case | Case style conditional, like an if. | case X; when Y; else; end |
| class | Define a new class. | class X; end |
| def | Define a new function. | def X(); end |
| defined? | Is this class/function/etc. defined already? | defined? Class == "constant" |
| do | Create a block that maybe takes a parameter. | (0..5).each do |x| puts x end |
| else | Else conditional. | if X; else; end |
| elsif | Else if conditional | if X; elsif Y; else; end |
| end | Ends blocks, functions, classes, everything. | begin end # many others |
| ensure | Run this code whether an exception happens or not. | begin ensure end |
| for | For loop syntax. The .each syntax is preferred. | for X in Y; end |
| if | If conditional. | if X; end |
| in | In part of for-loops. | for X in Y; end |
| module | Define a new module. | module X; end |
| next | Skip to the next element of a .each iterator. | (0..5).each {|y| next } |
| not | Logical not. But use ! instead. | not true == false |
| or | Logical or. | puts "Hello" or "Goodbye" |
| redo | Rerun a code block exactly the same. | (0..5).each {|i| redo if i > 2} |
| rescue | Run this code if an exception happens. | begin rescue X; end |
| retry | In a rescue clause, says to try the block again. | (0..5).each {|i| retry if i > 2} |
| return | Returns a value from a function. Mostly optional. | return X |
| self | The current object, class, or module. | defined? self == "self" |
| super | The parent class of this class. | super |
| then | Can be used with if optionally. | if true then puts "hi" end |
| undef | Remove a function definition from a class. | undef X |
| unless | Inverse of if. | unless false then puts "not" end |
| until | Inverse of while, execute block as long as false. | until false; end |
| when | Part of case conditionals. | case X; when Y; else; end |
| while | While loop. | while true; end |
| yield | Pause and transfer control to the code block. | yield |
Data Types
For data types, write out what makes up each one. For example, with strings write out how you create a string. For numbers write out a few numbers.
| TYPE | DESCRIPTION | EXAMPLE |
|---|---|---|
| true | True boolean value. | true or false == true |
| false | False boolean value. | false and true == false |
| nil | Represents “nothing” or “no value”. | x = nil |
| strings | Stores textual information. | x = "hello" |
| numbers | Stores integers. | i = 100 |
| floats | Stores decimals. | i = 10.389 |
| arrays | Stores a list of things. | j = [1,2,3,4] |
| hashes | Stores a key=value mapping of things. | e = {'x' => 1, 'y' => 2} |
String Escape Sequences
For string escape sequences, use them in strings to make sure they do what you think they do.
| ESCAPE | DESCRIPTION |
|---|---|
| \\ | Backslash |
| \' | Single-quote |
| \" | Double-quote |
| \a | Bell |
| \b | Backspace |
| \f | Formfeed |
| \n | Newline |
| \r | Carriage |
| \t | Tab |
| \v | Vertical tab |
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Operators
Some of these may be unfamiliar to you, but look them up anyway. Find out what they do, and if you still can’t figure it out, save it for later.
| OPERATOR | DESCRIPTION | EXAMPLE |
|---|---|---|
| + | Add | 2 + 4 == 6 |
| - | Subtract | 2 - 4 == 2 |
| * | Multiply | 2 * 4 == 8 |
| ** | Power of | 2 ** 4 == 16 |
| / | Divide | 2 / 4.0 == 0.5 |
| % | Modulus | 2 % 4 == 2 |
| > | Greater than | 4 > 4 == false |
| . | Dot access | "1".to_i == 1 |
| :: | Colon access | Module::Class |
| [] | List brackets | [1,2,3,4] |
| ! | Not | !true == false |
| < | Less than | 4 < 4 == false |
| > | Greater than | 4 < 4 == false |
| >= | Greater than equal | 4 >= 4 == true |
| <= | Less than equal | 4 <= 4 == true |
| <=> | Comparison | 4 <=> 4 == 0 |
| == | Equal | 4 == 4 == true |
| === | Equality | 4 === 4 == true |
| != | Not equal | 4 != 4 == false |
| && | Logical and (higher precedence) | true && false == false |
| || | Logical or (higher precedence) | true || false == true |
| .. | Range inclusive | (0..3).to_a == [0, 1, 2, 3] |
| ... | Range non-inclusive | (0...3).to_a == [0, 1, 2] |
| @ | Object scope | @var ; @@classvar |
| @@ | Class scope | @var ; @@classvar |
| $ | Global scope | $stdin |