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<h1 align="center">Ruby FAQ</h1>
<p align="right">September 27, 1999</p>
<p>
<h2><a name="toc1">1.</a><a href="rubyfaq-1.html">
General questions
</a></h2>
<ul>
<li><a href="rubyfaq-1.html#ss1.1">1.1
What is Ruby?
</a></li>
<li><a href="rubyfaq-1.html#ss1.2">1.2
What does Ruby stand for?
</a></li>
<li><a href="rubyfaq-1.html#ss1.3">1.3
Teach me the Ruby history.
</a></li>
<li><a href="rubyfaq-1.html#ss1.4">1.4
Where is it available?
</a></li>
<li><a href="rubyfaq-1.html#ss1.5">1.5
Where is the Home Page of Ruby?
</a></li>
<li><a href="rubyfaq-1.html#ss1.6">1.6
Is there a Ruby mailing list?
</a></li>
<li><a href="rubyfaq-1.html#ss1.7">1.7
How can I search past mails of the mailing list?
</a></li>
<li><a href="rubyfaq-1.html#ss1.8">1.8
What is the difference between rubyist and Ruby hacker?
</a></li>
<li><a href="rubyfaq-1.html#ss1.9">1.9
Which is authentic, Ruby or ruby?
</a></li>
<li><a href="rubyfaq-1.html#ss1.10">1.10
Is there a Ruby book?
</a></li>
<li><a href="rubyfaq-1.html#ss1.11">1.11
I cannot understand Ruby even after reading the manual.
</a></li>
</ul>
<p>
<h2><a name="toc2">2.</a><a href="rubyfaq-2.html">
Variables, constants and arguments
</a></h2>
<ul>
<li><a href="rubyfaq-2.html#ss2.1">2.1
Does assignment to a variable or a constant generate a new copy of an object?
</a></li>
<li><a href="rubyfaq-2.html#ss2.2">2.2
What is the definition of the scope of a local variable?
</a></li>
<li><a href="rubyfaq-2.html#ss2.3">2.3
When does a local variable become accessible?
</a></li>
<li><a href="rubyfaq-2.html#ss2.4">2.4
What is the definition of the scope of a constant?
</a></li>
<li><a href="rubyfaq-2.html#ss2.5">2.5
How is the actual argument passed to the formal argument?
</a></li>
<li><a href="rubyfaq-2.html#ss2.6">2.6
Does assignment to the formal argument influence the actual argument?
</a></li>
<li><a href="rubyfaq-2.html#ss2.7">2.7
What happens if I send a message to the object pointed by the formal argument
</a></li>
<li><a href="rubyfaq-2.html#ss2.8">2.8
What is the <code>*</code> prepended to an argument?
</a></li>
<li><a href="rubyfaq-2.html#ss2.9">2.9
What is the <code>&</code> prepended to an argument?
</a></li>
<li><a href="rubyfaq-2.html#ss2.10">2.10
Can I define a default value for a formal argument?
</a></li>
<li><a href="rubyfaq-2.html#ss2.11">2.11
How to pass arguments to a block.
</a></li>
<li><a href="rubyfaq-2.html#ss2.12">2.12
An unexpected change happens to the content of variables or constants.
</a></li>
<li><a href="rubyfaq-2.html#ss2.13">2.13
Does the value of a constant ever change?
</a></li>
</ul>
<p>
<h2><a name="toc3">3.</a><a href="rubyfaq-3.html">
Iterators
</a></h2>
<ul>
<li><a href="rubyfaq-3.html#ss3.1">3.1
What is an iterator?
</a></li>
<li><a href="rubyfaq-3.html#ss3.2">3.2
How can I pass a block to an iterator?
</a></li>
<li><a href="rubyfaq-3.html#ss3.3">3.3
How is a block used in an iterator?
</a></li>
<li><a href="rubyfaq-3.html#ss3.4">3.4
What does <code>Proc.new</code> without a block do?
</a></li>
</ul>
<p>
<h2><a name="toc4">4.</a><a href="rubyfaq-4.html">
Syntax
</a></h2>
<ul>
<li><a href="rubyfaq-4.html#ss4.1">4.1
What does <code>:exit</code> mean?
</a></li>
<li><a href="rubyfaq-4.html#ss4.2">4.2
How can I access the value of a symbol?
</a></li>
<li><a href="rubyfaq-4.html#ss4.3">4.3
Is <code>loop</code> a control structure?
</a></li>
<li><a href="rubyfaq-4.html#ss4.4">4.4
<code>a +b</code> gives an error.
</a></li>
<li><a href="rubyfaq-4.html#ss4.5">4.5
<code>s = "x"; puts s *10</code> gives an error.
</a></li>
<li><a href="rubyfaq-4.html#ss4.6">4.6
Nothing appears with <code>p {}</code>.
</a></li>
<li><a href="rubyfaq-4.html#ss4.7">4.7
After <code>def pos= (val) print @pos,"\n"; @pos = val end</code>,
I cannot use the method <code>pos = 1</code>.
</a></li>
<li><a href="rubyfaq-4.html#ss4.8">4.8
What is the difference between <code>'\1'</code> and <code>'\\1'</code>?
</a></li>
<li><a href="rubyfaq-4.html#ss4.9">4.9
<code>p true or true and false</code> prints <code>true</code>, while
<code>a=true if true or true and false</code> does not assign <code>true</code>
to <code>a</code>.
</a></li>
<li><a href="rubyfaq-4.html#ss4.10">4.10
<code>p(nil || "")</code> returns "", while <code>p(nil or "")</code>
gives parse error.
</a></li>
</ul>
<p>
<h2><a name="toc5">5.</a><a href="rubyfaq-5.html">
Methods
</a></h2>
<ul>
<li><a href="rubyfaq-5.html#ss5.1">5.1
How is the method searched when a messeage is sent to an object?
</a></li>
<li><a href="rubyfaq-5.html#ss5.2">5.2
Are <code>+</code> and <code>-</code> operators?
</a></li>
<li><a href="rubyfaq-5.html#ss5.3">5.3
Are there any functions?
</a></li>
<li><a href="rubyfaq-5.html#ss5.4">5.4
Can I access an object instance variable?
</a></li>
<li><a href="rubyfaq-5.html#ss5.5">5.5
I cannot figure out the difference between <code>private</code> and
<code>protected</code>.
</a></li>
<li><a href="rubyfaq-5.html#ss5.6">5.6
I want to make an instance variable public.
</a></li>
<li><a href="rubyfaq-5.html#ss5.7">5.7
How can I change the visibility of a method?
</a></li>
<li><a href="rubyfaq-5.html#ss5.8">5.8
Can I use an idenfier beginning with a capital letter for
a method name?
</a></li>
<li><a href="rubyfaq-5.html#ss5.9">5.9
<code>super</code> yields an <code>ArgumentError</code>.
</a></li>
<li><a href="rubyfaq-5.html#ss5.10">5.10
How can I call the same name method of two levels upper?
</a></li>
<li><a href="rubyfaq-5.html#ss5.11">5.11
How can I invoke the original built-in method after redfining it?
</a></li>
<li><a href="rubyfaq-5.html#ss5.12">5.12
What is a destructive method?
</a></li>
<li><a href="rubyfaq-5.html#ss5.13">5.13
When does an adverse effect occur using a method?
</a></li>
<li><a href="rubyfaq-5.html#ss5.14">5.14
Can I return multiple values from a method?
</a></li>
</ul>
<p>
<h2><a name="toc6">6.</a><a href="rubyfaq-6.html">
Classes and modules
</a></h2>
<ul>
<li><a href="rubyfaq-6.html#ss6.1">6.1
Can a class definition be repeated?
</a></li>
<li><a href="rubyfaq-6.html#ss6.2">6.2
Is there a class variable?
</a></li>
<li><a href="rubyfaq-6.html#ss6.3">6.3
What is a class instance variable?
</a></li>
<li><a href="rubyfaq-6.html#ss6.4">6.4
What is a singleton method?
</a></li>
<li><a href="rubyfaq-6.html#ss6.5">6.5
Is there a class method?
</a></li>
<li><a href="rubyfaq-6.html#ss6.6">6.6
What is a singleton class?
</a></li>
<li><a href="rubyfaq-6.html#ss6.7">6.7
What is a module function?
</a></li>
<li><a href="rubyfaq-6.html#ss6.8">6.8
What is the difference between a class and a module?
</a></li>
<li><a href="rubyfaq-6.html#ss6.9">6.9
Does a module generate a subclass?
</a></li>
<li><a href="rubyfaq-6.html#ss6.10">6.10
What is the difference between defining a class method in the class definition and directly at the toplevel?
</a></li>
<li><a href="rubyfaq-6.html#ss6.11">6.11
What is the difference between <code>load</code> and <code>require</code>?
</a></li>
<li><a href="rubyfaq-6.html#ss6.12">6.12
What is the difference between <code>include</code> and <code>extend</code>?
</a></li>
<li><a href="rubyfaq-6.html#ss6.13">6.13
What does <code>self</code> mean?
</a></li>
</ul>
<p>
<h2><a name="toc7">7.</a><a href="rubyfaq-7.html">
Builtin libraries
</a></h2>
<ul>
<li><a href="rubyfaq-7.html#ss7.1">7.1
What is the return value of <code>instance_methods(nil)</code>?
</a></li>
<li><a href="rubyfaq-7.html#ss7.2">7.2
Why does <code>rand</code> generate the same random number sequence?
</a></li>
<li><a href="rubyfaq-7.html#ss7.3">7.3
How can I choose 5 different numbers between 0 and 51 randomly?
</a></li>
<li><a href="rubyfaq-7.html#ss7.4">7.4
As <code>Fixnum</code>, <code>true</code>, <code>nil</code>, and <code>false</code>
are implemented as immediate values, what is the difference between
an immediate value and a reference?
</a></li>
<li><a href="rubyfaq-7.html#ss7.5">7.5
What is the difference between <code>nil</code> and <code>false</code>?
</a></li>
<li><a href="rubyfaq-7.html#ss7.6">7.6
I read a file and changed the content, but the file does not change.
</a></li>
<li><a href="rubyfaq-7.html#ss7.7">7.7
How can I read a file and replace it with new one?
</a></li>
<li><a href="rubyfaq-7.html#ss7.8">7.8
I wrote a file and copied the file, but the tail of the copied file is truncated.
</a></li>
<li><a href="rubyfaq-7.html#ss7.9">7.9
How can I use <code>less</code> to display strings?
</a></li>
<li><a href="rubyfaq-7.html#ss7.10">7.10
What occurs to a <code>File</code> object which has no reference?
</a></li>
<li><a href="rubyfaq-7.html#ss7.11">7.11
I feel uneasy if I don't close a file.
</a></li>
<li><a href="rubyfaq-7.html#ss7.12">7.12
How can I sort files by their modified time?
</a></li>
<li><a href="rubyfaq-7.html#ss7.13">7.13
How can I count word frequency in a file?
</a></li>
<li><a href="rubyfaq-7.html#ss7.14">7.14
Null string ("") returns <code>true</code> in a condition expression.
</a></li>
<li><a href="rubyfaq-7.html#ss7.15">7.15
How can I sort strings in alphabetical order?
</a></li>
<li><a href="rubyfaq-7.html#ss7.16">7.16
What does <code>"abcd"[0]</code> return?
</a></li>
<li><a href="rubyfaq-7.html#ss7.17">7.17
How can I expand tabs to spaces?
</a></li>
<li><a href="rubyfaq-7.html#ss7.18">7.18
How can I escape a backslash?
</a></li>
<li><a href="rubyfaq-7.html#ss7.19">7.19
What is the difference between <code>sub</code> and <code>sub!</code>?
</a></li>
<li><a href="rubyfaq-7.html#ss7.20">7.20
Where does \Z match?
</a></li>
<li><a href="rubyfaq-7.html#ss7.21">7.21
What is the difference between Range constructors <code>..</code> and <code>...</code>?
</a></li>
<li><a href="rubyfaq-7.html#ss7.22">7.22
Is there a function pointer?
</a></li>
<li><a href="rubyfaq-7.html#ss7.23">7.23
What is the difference between <code>thread</code> and <code>fork</code>?
</a></li>
<li><a href="rubyfaq-7.html#ss7.24">7.24
How can I use Marshal?
</a></li>
<li><a href="rubyfaq-7.html#ss7.25">7.25
Is there an exception handling?
</a></li>
<li><a href="rubyfaq-7.html#ss7.26">7.26
How can I use <code>trap</code>?
</a></li>
</ul>
<p>
<h2><a name="toc8">8.</a><a href="rubyfaq-8.html">
Extension library
</a></h2>
<ul>
<li><a href="rubyfaq-8.html#ss8.1">8.1
How can I use Ruby interactively?
</a></li>
<li><a href="rubyfaq-8.html#ss8.2">8.2
Is there a debugger for Ruby?
</a></li>
<li><a href="rubyfaq-8.html#ss8.3">8.3
How can I use a library written in C from Ruby?
</a></li>
<li><a href="rubyfaq-8.html#ss8.4">8.4
Can I use Tcl/Tk interface in Ruby?
</a></li>
<li><a href="rubyfaq-8.html#ss8.5">8.5
Tk won't work.
</a></li>
<li><a href="rubyfaq-8.html#ss8.6">8.6
Can I use <code>gtk+</code> or <code>xforms</code> interface in Ruby?
</a></li>
<li><a href="rubyfaq-8.html#ss8.7">8.7
How can I calculate dates?
</a></li>
</ul>
<p>
<h2><a name="toc9">9.</a><a href="rubyfaq-9.html">
Undocumented Features
</a></h2>
<ul>
<li><a href="rubyfaq-9.html#ss9.1">9.1
What does <code>a ? b : c</code> mean?
</a></li>
<li><a href="rubyfaq-9.html#ss9.2">9.2
How can I count the number of lines in a file?
</a></li>
<li><a href="rubyfaq-9.html#ss9.3">9.3
What do <code>begin</code> and <code>end</code> of MatchingData return?
</a></li>
</ul>
<p>
Originally written by Shugo Maeda
<code><a href="mailto:shugo@netlab.co.jp">
shugo@netlab.co.jp
</a></code>
<br>
Transformed to SGML by Ozawa Sakuro
<code><a href="mailto:crouton@duelists.org">
crouton@duelists.org</a></code>
<br>
Translated into English by gotoken
<code><a href="mailto:gotoken@math.sci.hokudai.ac.jp">
gotoken@math.sci.hokudai.ac.jp</a></code>
<br>
Revised by Akira Endo
<code><a href="mailto:akendo@t3.rim.or.jp">
akendo@t3.rim.or.jp</a></code>
<br>
since June 7, 1999 (original Sep 18, 1997)
<br>
Transformed to private XML on June 28, 1999, parsed with xmlparser by
Yoshida Masato<code><a href="mailto:yoshidam@inse.co.jp">
yoshidam@inse.co.jp</a></code>, <code><a href="yoshidam@yoshidam.net">
yoshidam@yoshidam.net</a></code>.
</p>
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