Ruby programming introduction

What is Ruby?

• An interpreted language • a.k.a dynamic, scripting • e.g., perl

• Object Oriented • Single inheritance

• High level • Good support for system calls, regex and CGI

• Relies heavily on convention for syntax

Hello World #!/usr/bin/env ruby puts “Hello world”

• shell script directive to run ruby • Needed to run any shell script

• Call to method puts to write out “Hello world” with CR $ chmod a+x helloWorld.rb $ helloWorld.rb Hello world $

• Make program executable

Basic Ruby • Everything is an object • Variables are not typed • Automatic memory allocation and garbage collection • Comments start with # and go to the end of the line • You have to escape \# if you want them elsewhere

• Carriage returns mark the end of statements • Methods marked with def … end

Control structures If…elsif…else…end case when <condition> then <value>… else… end

• elsif keeps blocks at same level • case good for checks on multiple values of same expression; can use ranges

unless <condition> … end while <condition>… end until <condition>… end

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

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

• Looping constructs use end (same as class definitions)

<collection>.each {block}

• Various iterators allow code blocks to be run multiple times

Ruby Naming Conventions • Initial characters

• Local variables, method parameters, and method names  lowercase letter or underscore • Global variable  $ • Instance variable  @ • Class variable  @@ • Class names, module names, constants  uppercase letter

• Multi-word names

• Instance variables  separate words with underscores • Class 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 Example class Temperature Factor = 5.0/9 def store_C(c) @celsius = c end

Factor is a constant 5.0 makes it a float

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

4 methods that get/set an instance variable

def as_C @celsius end def as_F (@celsius / Factor) + 32 end end # end of class definition

Last evaluated statement is considered the return value

Second Try class Temperature Factor = 5.0/9 attr_accessor :c def f=(f) @c = (f - 32) * Factor end

attr_accessor creates setter and getter methods automatically for a class variable

def f (@c / Factor) + 32 end

initialize is the name for a classesâ&#x20AC;&#x2122; constructor

def initialize (c) @c = c end end t = Temperature.new(25) puts t.f # 77.0 t.f = 60 # invokes f=() puts t.c # 15.55

Donâ&#x20AC;&#x2122;t worry - you can always override these methods if you need to Calls to methods donâ&#x20AC;&#x2122;t need () if unambiguous

Input and Output - tsv files f = File.open ARGV[0] while ! f.eof? line = f.gets if line =~ /^#/ next elsif line =~ /^\s*$/ next else puts line end end f.close

ARGV is a special array holding the commandline tokens Gets a line If itâ&#x20AC;&#x2122;s not a comment or a blank line Print it

Processing TSV files

h = Hash.new f = 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] end end f.close

keys = h.keys.sort {|a,b| a <=> b} keys.each {|k| puts "#{k}\t#{h[k]}" }

Declare a hash table Get lines without \n or \r\n - chomp split lines into fields delimited with tabs Store some data from each field into the hash Sort the keys - sort method takes a block of code as input each creates an iterator in which k is set to a value at each pass #{â&#x20AC;Ś} outputs the evaluated expression in the double quoted string

Blocks • Allow passing chunks of code in to methods • Receiving method uses “yield” command to call passed code (can call yield multiple times) • Single line blocks enclosed in {} • Multi-line blocks enclosed in do…end • Can use parameters [ 1, 3, 4, 7, 9 ].each {|i| puts i } Keys = h.keys.sort {|a,b| a <=> b }

Running system commands require '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}` end end

• curl is a command in mac os to retrieve a URL to a file, like wget in unix

• require 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 instances • We create a new variable to hold a new filename with the same base but different .html extension • We use backticks `` to run a system command and (optionally) save the output into a variable

CGI example require '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 <<FORM Content-type: text/html <HTML><BODY><FORM> Enter your name: <INPUT TYPE=TEXT NAME=t><INPUT TYPE=SUBMIT> </FORM></BODY></HTML> FORM end

• CGI requires library • Create CGI object • If parameters passed

• Process variable t • untaint variables if using them in commands

• No parameters?

• create form using here document “<<“

Reflection ...to examine aspects of the program from within the program itself. #print out all of the objects in our system ObjectSpace.each_object(Class) {|c| puts c} #Get all the methods on an object â&#x20AC;&#x153;Some Stringâ&#x20AC;?.methods #see if an object responds to a certain method obj.respond_to?(:length) #see if an object is a type obj.kind_of?(Numeric) obj.instance_of?(FixNum)