Reference: http://tryruby.org/

Interactive prompt

To open an interactive prompt on Mac OS X type: irb

Some simple functions

"Jimmy".reverse to reverse a string
"Jimmy".length to get the length of a string
"Jimmy" * 5

Conversions

40.to_s.reverse. You can't reverse a number, but you can if you convert to a string first. Reverse is not defined for numbers. It is defined for arrays.

  • to_s converts to strings
  • to_i converts to integers
  • to_a converts to arrays (or lists)

Lists

[] defines an empty list [12,47,35]­.max to get the maximum number in a list of integers
[12,47,35].sort to sort them
ticket = [12,47,35] will assign the list to a variable called ticket
ticket.sort will output the list sorted, but the value of ticket remains unchanged
ticket.sort! will sort the list and reassign it to ticket

Strings

poem["am"] = "was" will replace the first instance of am with was in the string variable poem poem.lines.to_a.reverse.join will break a multi-line string into lines, add them to an array, reverse the array, then join the elements of the array back together to once again make a string. to_s instead of join would also have worked.

Methods can sometimes use ! exclamation marks, and sometimes ? question marks.

Hashes

Hashes or dictionaries are created using {} e.g. books = {}.
This is actually short for Hash.new.
books.keys will return a list of all the keys in the hash.

Symbols

Instead of using the same words over and over, create a symbol using : e.g. :success.

Blocks

Blocks can be defined starting with an { and ending with }.
e.g. books.values.each { |rate| ratings[rate] += 1 }.

Blocks can alternatively be started with do and finished with end.

Files and directories

Dir.entries "/" gives an array of strings containing the names of all the directories or files in the root directory.
Dir["/*.txt"] will just list the text files in the root directory. This uses the [] method, similar to entries, but which searches for files using wildcard characters.
File.read(­"/comics.t­xt") will read the contents of the file.
Use FileUtils.­cp('/comic­s.txt', '/Hom­e/comics.t­xt') to copy files.
Open a file in append mode using add some lines:

File.open(­"/Home/com­ics.txt", "a") do |f|
f << "cat and girl"­  
end

Date and time

File.mtime("/Home/comics.txt") to find the last modified time of a file.
Time.now.hour to give just the hour.
Time.now - 2.weeks will give you the date 2 weeks ago.

Methods

Start with def, finish with end, indent if you like.

def load_comics( path )
  comics = {}
  File.foreach(path) do |line|
    name, url = line.split(': ')
    comics[name] = url.strip
  end
  comics
end

File.foreach is a method which opens a file and hands each line to the block.
require 'popu­p' if you need to import a library called popup. It will be loaded into the Libraries folder.

Classes

Simple class definition:

class BlogE­ntry
  attr_acces­sor :titl­e, :time­, :full­text, :mood­
end

Add a constructor:

class BlogEntry
  def initialize( title, mood, fulltext )
    @time = Time.now
    @title, @mood, @fulltext = title, mood, fulltext
  end
end

Accessors can be used outside the object using normal dot notation e.g. entry.title.
When inside the object prepend the @ symbol. e.g. @title.

More on lists

sort_by can be used on a list of objects to sort them:
e.g. blog.sort_­by { |entr­y| entry­.time }
e.g. blog.sort_­by { |entr­y| entry­.time }.reverse
map can be used to replace certain elements in a list e.g. blog.map {"Bruce Willis"} will replace each BlogEntry object in the list with a string