Ruby notes-basic(1)

Semicolons and newline characters are interpreted as ending of a statement. +, = or \ can be use as line continuation characters.
Comments
Single-line comments: Comments extend from # to the end of a line.
Multi-line comments:

=begin
comments go here
=end

Note: '=begin' and '=end' must appear at the beginning of a line.
Integer literals: 123, 0123(octal), 0xf34(hex), 0b1123(binary), ?d(char code for 'd')
Float-point literals: 23.45, 3e4, 4E10, 5e+39
String literals:
double quotations: allow substitution and escape character sequences.
single quotations: don't allow substitution and escape character sequences except \\ and \'.
Adjacent strings are concatenated automatically. "abc""def" => "abcdef"
Command execution: `command`. The syntax is similar to the counterpart of bash. It allows substituion and escape character sequences. The output generated by execution of the command is converted to a string.
here documents:

<<EOF content goes here EOF	The string is in double quotations.
<<"EOF" content goes here EOF
<<'EOF' content goes here EOF	The string is in single quotations.
<<`EOF` command goes here EOF	The string is in back quotes.
<<-EOF command goes here EOF	The delimiter ('EOF' in this example) needs not be at the beginning of a line.

Symbols:
"A symbol is an object corresponding to an identifier or variable"
:name    #symbol for 'name'
:$name   #symbol for variable 'name'
Array
[], [1,2,3], [1,[2,3]]
%w(str1 str2 str3) => ["str1", "str2", "str3"]
Dictionary(Map, or Hash):
{key => value}
Regular expression:
/pattern/
/pattern/options

Alternatives:
%!string! and %Q!string! are equivalent to "string".
%q!string! is equivalent to 'string'
%x!command! is equivalent to `command`.
%r!pattern!

Variable

Type	Description	Example	Note
global variables	can be accessed globally by and program.	$var	Uninitialized global variables are set to nil.
instance	variables that belong to an object.	@var
class	variables that belong to a class.	@@var	Class variables must be initialized before they are accessed in methods.
contants	Constants as you know in other languages	Var	must begin with an upper case letter.May not be defined in methods.
local	Local variables.	var	must begin with a lowercase letter or _

Variable substitutions: #{varname}. E.g. #{filename}, #{@conf}, #{$stdin} 
Variable assignments
var = value
var1, var2, ..., *varn = expr1, expr2, ..., *exprn
Operators:

expr?expr1:expr2

    The same as the tertiary operator in C/C++.

defined? varname

    #return a description about the variable/method or nil.

Control statements

Name	Syntax	Alternatives
if	if cond [then]     code [elsif cond [then]     code] [else     code] end	code if cond
unless	unless cond [then]     code [else     code] end	code unless cond
case	case expr [when expr [,expr ...] [then]     code ]... [else     code] end
while	while cond [do]     code end	(1)code while cond (2)begin code end while cond. Note: code is executed once before cond is evaluated.
until	until cond [do]     code end	(1) code until cond (2) begin code end until cond Note: code is executed once before cond is evaluated.
for	for var[, var2 ...] in expr [do]     code end	expr do |var [,var...]|     code end
break	Break from look
next	like continue in C++
redo	re-execute the loop body once without evaluation of conditional expression.
retry	re-execute a call to a method
begin	begin     code [rescue [exception_class [, excep_cls...]] [=>var] [then]     code ]... [else     code ] [ensure     code ] end	Code in ensure clause is always executed. Code in else clause is executed only when no exceptions are raised. Code in rescue clause is executed when exception is caught.
rescue	code rescue expr	Evaluate the expr only if an exception is caught.
raise	raise exception_class, message raise exception_object raise message raise	Raise an exception. To call raise in a rescue clause will re-raise the exception.
BEGIN	BEGIN{     code }	Code to be executed before the program is run.
END	END{     code }	Code to be executed when the interpreter quits.