Rootroute ruby language pages

The Ruby Language FAQ

Originally by: Shugo Maeda. Now maintained by Dave Thomas with help from Andy Hunt.

1. General questions

• 1.1 What is Ruby?
• 1.2 Show me some Ruby code.
• 1.3 Why the name 'Ruby'?
• 1.4 What is the history of Ruby?
• 1.5 Where is the Ruby Home Page?
• 1.6 Is there a Ruby newsgroup?
• 1.7 Is there a Ruby mailing list?
• 1.8 **Changed** How can I thread the mailing list in mutt?
• 1.9 Which is correct, Ruby or ruby?
• 1.10 Are there any Ruby books?
• 1.11 Which editors provide support for Ruby.
• 1.12 How can I annotate Ruby code with its results?
• 1.13 I can't understand Ruby even after reading the manual!

2. How Does Ruby Stack Up Against...?

• 2.1 How Does Ruby Compare With Python?

3. Installing Ruby

• 3.1 What operating systems support Ruby?
• 3.2 Where can I get Ruby sources?
• 3.3 Can I get to the development source tree?
• 3.4 How do I compile Ruby?
• 3.5 **Changed** How do I tell Ruby where my libraries are?
• 3.6 Are precompiled binaries available?
• 3.7 What's all this 'cygwin', 'mingw', and 'djgpp' stuff?
• 3.8 Why doesn't Tk graphics work under Windows?

4. Variables, constants, and arguments

• 4.1 Does assignment generate a new copy of an object?
• 4.2 What is the scope of a local variable?
• 4.3 When does a local variable become accessible?
• 4.4 What is the scope of a constant?
• 4.5 How are arguments passed?
• 4.6 Does assignment to a formal argument influence the actual argument?
• 4.7 What happens when I invoke a method via a formal argument?
• 4.8 What does ``*'' prepended to an argument mean?
• 4.9 What does ``&'' prepended to an argument mean?
• 4.10 How can I specify a default value for a formal argument?
• 4.11 How do I pass arguments to a block?
• 4.12 Why did my object change unexpectedly?
• 4.13 Does the value of a constant ever change?

5. Iterators

• 5.1 What is an iterator?
• 5.2 How can I pass a block to an iterator?
• 5.3 How is a block used in an iterator?
• 5.4 What does Proc.new without a block do?
• 5.5 How can I run iterators in parallel?

6. Syntax

• 6.1 What does :var mean?
• 6.2 How can I access the value of a symbol?
• 6.3 Is loop a control structure?
• 6.4 Ruby doesn't have a post-test loop
• 6.5 a +b gives an error!
• 6.6 s = "x"; puts s *10 gives an error.
• 6.7 Why can't I pass a hash literal to a method: p {}?
• 6.8 I can't get def pos=(val) to work.
• 6.9 What is the difference between '\1' and '\\1'?
• 6.10 What's the difference between ``or'' and ``||''?

7. Methods

• 7.1 How does Ruby choose which method to invoke?
• 7.2 Are +, -, * ... operators?
• 7.3 Where are ++ and - -?
• 7.4 All these objects are fine, but does Ruby have any simple functions?
• 7.5 So where do all these function-like methods come from?
• 7.6 Can I access an object's instance variables?
• 7.7 What's the difference between private and protected?
• 7.8 How can I change the visibility of a method?
• 7.9 Can an identifier beginning with a capital letter be a method name?
• 7.10 Calling super gives an ArgumentError.
• 7.11 How can I call the a method of the same name two levels up?
• 7.12 How can I invoke an original built-in method after redefining it?
• 7.13 What is a destructive method?
• 7.14 Why can destructive methods be dangerous?
• 7.15 Can I return multiple values from a method?

8. Classes and modules

• 8.1 Can a class definition be repeated?
• 8.2 Are there class variables?
• 8.3 What is a class instance variable?
• 8.4 What is a singleton method?
• 8.5 Does Ruby have class methods?
• 8.6 What is a singleton class?
• 8.7 What is a module function?
• 8.8 What is the difference between a class and a module?
• 8.9 Can you subclass modules?
• 8.10 Give me an example of a mix-in
• 8.11 Why are there two ways of defining class methods?
• 8.12 What is the difference between load and require?
• 8.13 What is the difference between include and extend?
• 8.14 What does self mean?
• 8.15 Why can't I load variables from a separate file?

9. Builtin libraries

• 9.1 What does instance_methods(nil) return?
• 9.2 How do random number seeds work?
• 9.3 What is the difference between an immediate value and a reference?
• 9.4 What is the difference between nil and false?
• 9.5 I read a file and changed it, but the file on disk has not changed.
• 9.6 How can I process a file and update its contents?
• 9.7 I wrote a file, copied it, but the end of the copy seems to be lost.
• 9.8 How can I get the line number in current input file?
• 9.9 How can I use less to display my program's output?
• 9.10 What happens to a File object which is no longer referenced?
• 9.11 I feel uneasy if I don't close a file.
• 9.12 How can I sort files by their modified time?
• 9.13 How can I count the frequency of words in a file?
• 9.14 Why is an empty string not false?
• 9.15 How can I sort strings in alphabetical order?
• 9.16 What does "abcd"[0] return?
• 9.17 How can I expand tabs to spaces?
• 9.18 How can I escape a backslash in a regexp?
• 9.19 What is the difference between sub and sub!?
• 9.20 Where does \Z match?
• 9.21 What is the difference between ".." and "..."?
• 9.22 Does Ruby have function pointers?
• 9.23 What is the difference between thread and fork?
• 9.24 How can I use Marshal?
• 9.25 Does Ruby have exception handling?
• 9.26 How can I use trap?

10. Extension library

• 10.1 How can I use Ruby interactively?
• 10.2 Is there a debugger for Ruby?
• 10.3 How can I use a library written in C from Ruby?
• 10.4 Can I use Tcl/Tk interface in Ruby?
• 10.5 Tk won't work.
• 10.6 Can I use gtk+ or xforms interfaces in Ruby?
• 10.7 How can I do date arithmetic?

11. Other Features

• 11.1 What does a ? b : c mean?
• 11.2 How can I count the number of lines in a file?
• 11.3 What do begin and end of MatchingData return?
• 11.4 How can I sum the elements in an array?
• 11.5 How can I use continuations?