What is Ruby?An interpreted language a.k.a dynamic, scriptinge.g., perlObject OrientedSingle inheritanceHigh levelGood support for system calls, regex and CGIRelies heavily on convention for syntax

Hello World#!/usr/bin/env ruby

puts Hello world

$ chmod a+x helloWorld.rb$ helloWorld.rbHello world$ shell script directive to run rubyNeeded to run any shell scriptCall to method puts to write out Hello world with CR

Make program executable

Basic RubyEverything is an objectVariables are not typedAutomatic memory allocation and garbage collectionComments start with # and go to the end of the lineYou have to escape \# if you want them elsewhereCarriage returns mark the end of statementsMethods marked with def end

Control structuresIfelsifelseendcase when then else end

unless endwhile enduntil end

#.times (e.g. 5.times())#.upto(#) (e.g. 3.upto(6))

.each {block}elsif keeps blocks at same levelcase good for checks on multiple values of same expression; can use ranges

grade = case score when 90..100 then A when 80..90 then B else C end

Looping constructs use end (same as class definitions)

Various iterators allow code blocks to be run multiple times

Ruby Naming ConventionsInitial charactersLocal variables, method parameters, and method names lowercase letter or underscoreGlobal variable $Instance variable @Class variable @@Class names, module names, constants uppercase letterMulti-word namesInstance variables separate words with underscoresClass names use MixedCase End characters? Indicates method that returns true or false to a query! Indicates method that modifies the object in place rather than returning a copy (destructive, but usually more efficient)

Another Exampleclass Temperature Factor = 5.0/9

def store_C(c) @celsius = c end

def store_F(f) @celsius = (f - 32)*Factor end

def as_C @celsius end

def as_F (@celsius / Factor) + 32 endend # end of class definition Factor is a constant5.0 makes it a float

4 methods that get/set an instance variable

Last evaluated statement is considered the return value

Second Tryclass Temperature Factor = 5.0/9 attr_accessor :c

def f=(f) @c = (f - 32) * Factor end

def f (@c / Factor) + 32 end

def initialize (c) @c = c endend

t = Temperature.new(25)puts t.f # 77.0t.f = 60 # invokes f=()puts t.c # 15.55attr_accessor creates setter and getter methods automatically for a class variable

initialize is the name for a classes constructor

Dont worry - you can always override these methods if you need to

Calls to methods dont need () if unambiguous

Input and Output - tsv filesf = File.open ARGV[0]while ! f.eof? line = f.gets if line =~ /^#/ next elsif line =~ /^\s*$/ next else puts line endendf.closeARGV is a special array holding the command-line tokens

Gets a lineIf its not a comment or a blank linePrint it

Processing TSV filesh = Hash.newf = File.open ARGV[0]while ! f.eof? line = f.gets.chomp if line =~ /^\#/ next elsif line =~ /^\s*$/ next else tokens = line.split /\t/ h[tokens[2]] = tokens[1] endendf.close

keys = h.keys.sort {|a,b| a b}keys.each {|k| puts "#{k}\t#{h[k]}" }Declare a hash tableGet lines without \n or \r\n - chompsplit lines into fields delimited with tabsStore some data from each field into the hash

Sort the keys - sort method takes a block of code as inputeach creates an iterator in which k is set to a value at each pass#{} outputs the evaluated expression in the double quoted string

BlocksAllow passing chunks of code in to methodsReceiving method uses yield command to call passed code (can call yield multiple times)

Single line blocks enclosed in {}Multi-line blocks enclosed in doend

Can use parameters[ 1, 3, 4, 7, 9 ].each {|i| puts i }Keys = h.keys.sort {|a,b| a b }

Running system commandsrequire 'find'

Find.find('.') do |filename| if filename =~ /\.txt$/i url_output = filename.gsub(/\.txt$/i, ".html") url = `cat #{filename}`.chomp cmd = "curl #{url} -o #{url_output}"; puts cmd `#{cmd}` endendrequire reads in another ruby file - in this case a module called Find

Find returns an array, we create an iterator filename to go thru its instancesWe create a new variable to hold a new filename with the same base but different .html extensionWe use backticks `` to run a system command and (optionally) save the output into a variable curl is a command in mac os to retrieve a URL to a file, like wget in unix

CGI examplerequire 'cgi'

cgi = CGI.new("html3")size = cgi.params.size

if size > 0 # processing form in = cgi.params['t'].first.untaint cgi.out { cgi.html { cgi.head cgi.body { "Welcome, #{in}!" } } }else puts

Reflection...to examine aspects of the program from within the program itself.

#print out all of the objects in our systemObjectSpace.each_object(Class) {|c| puts c}

#Get all the methods on an objectSome String.methods

#see if an object responds to a certain methodobj.respond_to?(:length)

#see if an object is a typeobj.kind_of?(Numeric)obj.instance_of?(FixNum)

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