Rails Beginner Cheat Sheet

Front 1

cd

Back 1

Change directory, changes the directory to the specified directory on the console

Front 2

ls

Back 2

list contents directory, shows all content (files and folders) of the directory. If no directory is specified shows the contents of the current directory

Front 3

pwd

Back 3

directory you are currently in, shows the full path of the directory you are currently in

Front 4

mkdir

Back 4

create a new directory, creates a directory with the given name in the folder you are currently in

Front 5

rm

Back 5

delete a file, deletes the specified file

Front 6

rm -r

Back 6

delete a directory, deletes the specified folder and all of its contents

Front 7

program

Back 7

starting a program, starts the program with the given name and arbitrary arguments if the program takes arguments

Front 8

ctrl + c

Back 8

abort the program

Front 9

#

Back 9

comment

Front 10

variable=

Back 10

variables

Front 11

puts

Back 11

console output, prints its argument to the console. Can be used in Rails apps to print something in the console where the server is running

Front 12

object.method(arguments)

Back 12

call a method ( length, delete_at, or gsub) calling a method is also referred to as sending a message in Ruby.

Front 13

def name(parameter)

# method body

end

Back 13

define a method, methods are basically reusable units of behavior. And you can define them yourself

Front 14

object == other

Back 14

Equality; with two equal signs you can check if two things are the same. If so, true will be returned; otherwise, the result will be false

Front 15

object ! = other

Back 15

Inequality; Inequality is the inverse to equality, e.g. it results in true when two values are not the same and it results in false when they are the same

Front 16

if condition

# happens when true

else

# happens when false

end

Back 16

With if- clauses you can decide based upon a condition what to do. When the condition is considered true, then the code after it is executed. If it is considered false, the code after the "else" is executed

Front 17

constant = some_value

Back 17

Constants; constants look like variables, just in UPCASE. Both hold values and give you a name to refer to those values.

Front 18

number_of_your_choice

Back 18

normal Number,

Front 19

main.decimal

Back 19

Decimals, achieve decimal numbers in Ruby simply by adding a point

Front 20

n operator m

Back 20

Basic math; in Ruby you can easily use basic math operations. In that sense you may use Ruby as a super-powered calculator

Front 21

n operator m

Back 21

comparison (<> >=); numbers may be compared to determine if a number is bigger or smaller than another number

Front 22

"A String"

Back 22

Create; a string is created by putting quotation marks around a character sequence

Front 23

"A String and an #{expression}"

"Email: #{user.email}"

Back 23

Interpolation; you can combine a string with a variable or Ruby expression using double quotation marks

Front 24

string.length

"Hello".length# =>5

"".length #=>0

Back 24

you can send a string a message, asking how long it is and it will respond with the number of characters it consists of.

Front 25

string+string2

"Hello" + "reader"

# => "Hello reader"

Back 25

concatenate; concatenates two or more string together and returns the result

Front 26

string.gsub(a_string,substitute)

Back 26

substitute, gsub stands for "globally substitute". It substitutes all occurrences of a_string within the string with substitute.

Front 27

string[position]

"Hello"[1] # => "e"

Back 27

Access the character at the given position in the string. Be aware that the first position is actually position 0.

Front 28

[contents]

Back 28

creates an Array, empty or with the specified contents.

Front 29

array.size

[].size # => 0

[1, 2, 3].size # => 3

Back 29

returns the number of elements in an Array

Front 30

array[position]

array = ["hi", "foo", "bar"]

array[0] # => "hi"

Back 30

As an Array is a collection of different elements, you often want to access a single element of the Array. Arrays are indexed by numbers so you can use a number to access an individual element

Front 31

array << element

array = [1, 2, 3]

array << 4

array # => [1, 2, 3, 4]

Back 31

Adding an element; adds the element to the end of the array, increasing the size of the array by one

Front 32

array[number] = value

array = ["hi", "foo", "bar"]

array[2] = "new"

array # => ["hi", "foo", "new"]

Back 32

Assigning, Assigning new Array Values works a lot like accessing them; use an equals sign to set a new value.

Front 33

array.delete_at(i)

array = [0, 14, 55, 79]

array.delete_at(2)

array # => [0, 14, 79]

Back 33

Delete at Index; Deletes the element of the array at the specified index. Remember that indexing starts at 0.

Front 34

array.each do |e| .. end

persons.each do |p| puts p.name end

numbers.each do |n| n = n * 2 end

Back 34

Iterating, "Iterating" means doing something foreach element of the array. Code placed between do and end determines what is done to each element in the array.