Scripting with Ruby

1. What is a scripting language? What is Ruby? Scripting with Ruby

2. Scripting Languages Originally, a script was a file containing a sequence of commands that needed to be executed Control structures were added to make it possible to do more with scripts

3. Characteristics of Scripting Languages Generally interpreted Dynamic typing - no declarations Make text processing easy Often provide pattern matching for strings Provide file and directory manipulation Make it easy to do things quickly

4. Basic Scripting Languages Unix and Linux come with shell programs which are programmable sh bash ksh csh DOS had BAT files

5. Scripting in Other Environments Even with a GUI operating system, it is still useful to be able to automate repetitive tasks Windows still has bat files Mac OS has AppleScript Some applications have a scripting language built into them Microsoft applications have Visual Basic for Applications (VBA) Hypercard (Apple) had HyperTalk

6. Other Scripting Languages Other scripting languages were developed to provide increased capability sed -- adapted from the UNIX ed editor in 1977 AWK -- created by Ajo, Wienberger and Kernighan in 1977 Tcl -- an extensible scripting language written by John Ousterhout in 1987 Perl -- created by Larry Wall in 1986 Python-- created in 1989 by Guido van Rossum Ruby -- created in 1993 by Yukihiro Matsumoto

7. Scripting and the Web More recently, a number of scripting languages have been developed for use with web browsers PHP JavaScript Active Scripting provided scripting for web pages built using the ASP framework

8. Scripting on onyx the shell languages sed awk perl python ruby tcl javascript php

9. History • Written by Yukihiro “matz” Matsumoto • First released in 1995 • Blend of Perl, Smalltalk, Eiffel, Ada and Lisp

10. Ruby object-oriented everything is an object interpreted "syntax light" variables are dynamically typed variables are references to objects supports single inheritance mixins give some of benefits of multiple inheritance

11. Running a ruby program Run the interpreter by typing ruby prog.rb Make an executable script The first line should be #!/usr/bin/ruby Make the file executable and type its name to run it chmod +x prog.rb ./prog.rb Use the irb command to get an interactive session

12. Basic Syntax Program is a sequence of definitions and statements No semicolons at end of statement semicolons can separate statements on a single line Parentheses around method arguments are optional unless ambiguous Comments start with a #

13. Naming Conventions local variables, parameters and method names start with lower case letter or underscore class and module names and constants start with an uppercase letter instance variables start with @ class variables start with @@ global variables start with $

14. Numbers are objects Integer Fixnum Bignum Float Complex Ruby distinguishes between integers and floating point types Usual operators plus exponentiation Math class has usual selection of methods Integers can have an arbitrary number of digits Numbers in Ruby

15. Ranges Ruby has a class that represents subranges 1..10 'a'..'z' Can be used as conditions Operations to_a converts range to array include? tests for inclusion, also === min, max each is iterator reject is iterator that skips members based on some condition

16. Representing Text • A string is a sequence of characters • Original implementation was a simple array of bytes • Now consists of an array of bytes with an associated encoding • No separate type for a single character

17. Strings Literals can use either single or double quotes Variables can be interpolated in double-quoted strings "name = #{name}" Escape characters are replaced in double-quoted strings Single quoted strings can escape only \ and ' %q and %Q are alternate forms for single and double quoted strings Also, check out here documents

18. String Operations Strings can be concatenated with + both operands must be strings << concatenates another type of object * repeats the string a specified number of times == and === compare for equality <==> is like compare to [] indexes an element

19. String methods split, scan followed by optional regular expression tokenize string capitalize, capitalize!, downcase, downcase! include? index length

20. Regular Expressions Patterns enclosed between slashes /<pattern>/ Operator =~ means matches (returns boolean) Uses perl syntax

21. Arrays Creating create with literal Array.new creates an empty array Size can grow dynamically Slices can be retrieved and assigned Useful methods: concat, collect, delete, each, empty?, join, sort, dup

22. Hashes Creating Use a literal h = {'horse' => 'mammal', 'trout' => 'fish', 'frog' => 'amphibian'} Use new h2 = Hash.new can specify value of missing element as argument to new

23. Hash Methods default returns the default value (nil by default); can also be set delete, delete_if remove elements replace updates an element each, each_key, each_value iterate through the hash length returns number of entries has_key?, has_value? sort (by key), dup, …

24. I/O puts prints its argument followed by a newline print does not append a newline printf for formatted output gets reads a line default destination is $_

25. Boolean expressions • Anything that is not false or nil is true. • Note: 0 is not false • The logical operators are • and, && • or, || • not, ! • isDefined?

26. Relational Operators == equal value === case equality <=> like compareTo < <= >= > =~ matches eql? Compares values equal? Compares object id

27. Selection if statement if <condition> <statements> elsif <condition> <statements> else <statements> end if statement modifier <statement> if <condition> unless statement modifier <statement> unless <condition>

28. Case Expressions • Multiway selection case year when <range, boolean, pattern> end

29. Repetition while statement while <condition> <statements> end while statement modifier <statement> while <condition> until statement modifier <statement> until <condition>

30. Conditional Modifiers • There are four modifiers that can control whether a single statement gets executed • if • unless • while • until • The syntax is <statement> <modifier> <condition>

31. Blocks Chunk of code that can be passed to a method behaves like an anonymous (unnamed) function often used with iterators Two forms do <statements> end {|<paramlist>| <statements } A method can have a block as a parameter block is executed by typing yield

32. Iterators Blocks are used to implement iterators Pseudocode for typical iterator def each for each element yield element end end

33. Methods Return value of a method is the value of the last statement executed irb prints value of each statement it executes Syntax for defining def fnName <statements> end

34. Classes Attributes are private (@varname) attr_reader to sepcify accessors attr_writer to specify mutators Class variables (@@varname) methods called with class name private, protected, public access for methods

35. For more information David Thomas and Andrew Hunt, Programming Ruby, The Pragmatic Programmer's Guide, Addison Wesley David Flanagan and Yukihiro Matsumoto, The Ruby programming language in Safari Books online at library

36. On the Web • Ruby home page http://www.ruby-lang.org/en/ • 10 Things Every Java Programmer Should Know About Ruby http://onestepback.org/articles/10things/index.html