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

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

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

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

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

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

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

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

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

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

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 #

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 class variables start with global variables start with $

Numbers in Ruby 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

Ranges Ruby has a class that represents subranges '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

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

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

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

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

Regular Expressions Patterns enclosed between slashes / Operator =~ means matches (returns boolean) Uses perl syntax

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

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

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, dup, …

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 $_

Selection if statement if elsif else end if statement modifier if unless statement modifier unless

Repetition while statement while end while statement modifier while until statement modifier until

Conditional Modifiers There are four modifiers that can control whether a single statement gets executed – if – unless – while – until The syntax is

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

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

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 end

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

For more information David Thomas and Andrew Hunt, Programming Ruby, The Pragmatic Programmer's Guide, Addison Wesley Ruby home page