Symbols – Keywords, String Escape Sequences & Operators

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

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

 

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