Introduction to Ruby

1. Introduction to Ruby WING Group Meeting 9 Jun 2006 Min-Yen Kan

2. 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

3. #!/usr/bin/env ruby puts “Hello world” $ chmod a+x helloWorld.rb $ helloWorld.rb 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 Make program executable Hello World

4. 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

5. If…elsif…else…end case when <condition> then <value>… else… end unless <condition> … end while <condition>… end until <condition>… end #.times (e.g. 5.times()) #.upto(#) (e.g. 3.upto(6)) <collection>.each {block} elsif keeps blocks at same level case 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 Control structures

6. 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)

7. class 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 end end # end of class definition Factor is a constant 5.0 makes it a float 4 methods that get/set an instance variable Last evaluated statement is considered the return value Another Example

8. class 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 end end t = Temperature.new(25) puts t.f # 77.0 t.f = 60 # invokes f=() puts t.c # 15.55 attr_accessor creates setter and getter methods automatically for a class variable initialize is the name for a classes’ constructor Don’t worry - you can always override these methods if you need to Calls to methods don’t need () if unambiguous Second Try

9. /[A-Z]/i /[^>]+/ /<A[^>]+/im /<A[^>]+>.*<\/A>/im /[^\t]/ /([^\t]+)/ /^([^\t]+)\t([^\t]+)$/ First class objects in ruby Sandwiched between // Quiz: How do you make a regexp for <A>…</A>? Regular Expressions

10. 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 command-line tokens Gets a line If it’s not a comment or a blank line Print it Input and Output - tsv files

11. 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 #{…} outputs the evaluated expression in the double quoted string Processing TSV files

12. 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 }

13. 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 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 Running system commands • curl is a command in mac os to retrieve a URL to a file, like wget in unix

14. 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 “<<“ CGI example

15. 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 “Some String”.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)

16. Summary • High-level interpreted OO language • No types; objects can reflect • Native support of regex, iterators, system calls and CGI • Relies on convention to limit variability • OO encourages modular, maintainable code (if needed) • Strong support for CGI and unit testing Only the basic here, multiple inheritance, exception handling, threading and testing are not covered

17. Modules • Marshal - serialize data for load/save between program executions • Date • GetOptLong - manipulate command line arguments and switches • Tempfile • Mutex - semaphores for parallel code • Net::URI • Socket - different socket types • CGI • CGI::Session

18. rdoc - ruby javadoc rake - ruby make eruby - embedded ruby (in HTML; think php) rubygems - ruby package manager Irb - interactive ruby (good for debugging) Ruby on Rails (rails) For building web applications Based on Model-View-Contoller architecture further integration of ruby with database backend Programming Rubyby Dave Thomas (the Pickaxe Book) http://www.ruby-lang.org http://www.rubyforge.org http://www.rubycentral.org http://www.ruby-doc.org http://www.rubygarden.org http://www.stlruby.org http://www.rubyquiz.com http://www.zenspider.com/Languages/Ruby/QuickRef.html References