Ruby programming introduction

Ruby programming introduction

• 1.
  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
• 2.
  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
• 3.
  Basic Ruby •Everything isan 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
• 4.
  Control structures 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
• 5.
  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)
• 6.
  Another Example 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
• 7.
  Second Try 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
• 8.
  Input and Output- tsv files f = File.open ARGV[0] while ! f.eof? line = f.gets if line =~ /^#/ next elsif line =~ /^s*$/ next else puts line end end f.close ARGV is a special array holding the command- line tokens Gets a line If it’s not a comment or a blank line Print it
• 9.
  Processing TSV filesh= Hash.new f = File.open ARGV[0] while ! f.eof? line = f.gets.chomp if line =~ /^#/ next elsif line =~ /^s*$/ 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 rn - 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
• 10.
  Blocks •Allow passing chunksof 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 }
• 11.
  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 • 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
• 12.
  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 <<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 “<<“
• 13.
  Reflection ...to examine aspectsof 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)