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

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 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” $ chmod a+x helloWorld.rb $ helloWorld.rb Hello world $ #!/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

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 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 then … else… end unless … end while … end until … end #.times (e.g. 5.times()) #.upto(#) (e.g. 3.upto(6)).each {block} If…elsif…else…end case when then … else… end unless … end while … end until … end #.times (e.g. 5.times()) #.upto(#) (e.g. 3.upto(6)).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 then “A” when 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 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) 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 = c end def = (f - 32)*Factor end def end def as_F / Factor) + 32 end end # end of class definition class Temperature Factor = 5.0/9 def = c end def = (f - 32)*Factor end def end def as_F / 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

Second Try class Temperature Factor = 5.0/9 attr_accessor :c def = (f - 32) * Factor end def f / Factor) + 32 end def initialize = c end t = Temperature.new(25) puts t.f # 77.0 t.f = 60 # invokes f=() puts t.c # class Temperature Factor = 5.0/9 attr_accessor :c def = (f - 32) * Factor end def f / Factor) + 32 end def initialize = c end t = Temperature.new(25) puts t.f # 77.0 t.f = 60 # invokes f=() puts t.c # 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

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

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

Processing TSV files h = Hash.new f = File.open ARGV[0] while ! f.eof? line = f.gets.chomp if line =~ /^\#/ next elsif line =~ /^\s*$/ next else tokens = line.split /\t/ h[tokens[2]] = tokens[1] end f.close keys = h.keys.sort {|a,b| a b} keys.each {|k| puts "#{k}\t#{h[k]}" } h = Hash.new f = File.open ARGV[0] while ! f.eof? line = f.gets.chomp if line =~ /^\#/ next elsif line =~ /^\s*$/ next else tokens = line.split /\t/ h[tokens[2]] = tokens[1] end 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

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

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 Enter your name: <INPUT TYPE=TEXT NAME=t> FORM end 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 Enter your name: <INPUT TYPE=TEXT NAME=t> 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 “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)...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)

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 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

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 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

References 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 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 Ruby by Dave Thomas (the Pickaxe Book) ges/Ruby/QuickRef.html