begin 
# - 
rescue OneTypeOfException 
# - 
rescue AnotherTypeOfException 
# - 
else 
# 其他异常
ensure
# 总是被执行
end

#!/usr/bin/ruby
 
begin
  file = open("/unexistant_file")
  if file
   puts "File opened successfully"
  end
rescue
   file = STDIN
end
print file, "==", STDIN, "n"

begin
  # 这段代码抛出的异常将被下面的 rescue 子句捕获
rescue
  # 这个块将捕获所有类型的异常
  retry # 这将把控制移到 begin 的开头
end
实例
#!/usr/bin/ruby
 
begin
  file = open("/unexistant_file")
  if file
   puts "File opened successfully"
  end
rescue
  fname = "existant_file"
  retry
end

raise
 
OR
 
raise "Error Message"
 
OR
 
raise ExceptionType, "Error Message"
 
OR
 
raise ExceptionType, "Error Message" condition

#!/usr/bin/ruby
 
begin 
  puts 'I am before the raise.' 
  raise 'An error has occurred.' 
  puts 'I am after the raise.' 
rescue 
  puts 'I am rescued.' 
end 
puts 'I am after the begin block.' 

I am before the raise. 
I am rescued. 
I am after the begin block. 

#!/usr/bin/ruby
 
begin 
 raise 'A test exception.' 
rescue Exception => e 
 puts e.message 
 puts e.backtrace.inspect 
end 

A test exception.
["main.rb:4"]

begin
  #.. 过程
  #.. 抛出异常
rescue
  #.. 处理错误
ensure
  #.. 最后确保执行
  #.. 这总是会执行
end
实例
begin
 raise 'A test exception.'
rescue Exception => e
 puts e.message
 puts e.backtrace.inspect
ensure
 puts "Ensuring execution"
end

A test exception.
["main.rb:4"]
Ensuring execution

begin
  #.. 过程
  #.. 抛出异常
rescue
  #.. 处理错误
else
  #.. 如果没有异常则执行
ensure
  #.. 最后确保执行
  #.. 这总是会执行
end
实例
begin
 # 抛出 'A test exception.'
 puts "I'm not raising exception"
rescue Exception => e
 puts e.message
 puts e.backtrace.inspect
else
  puts "Congratulations-- no errors!"
ensure
 puts "Ensuring execution"
end

I'm not raising exception
Congratulations-- no errors!
Ensuring execution

throw :lablename
#.. 这不会被执行
catch :lablename do
#.. 在遇到一个 throw 后匹配将被执行的 catch
end
 
OR
 
throw :lablename condition
#.. 这不会被执行
catch :lablename do
#.. 在遇到一个 throw 后匹配将被执行的 catch
end

def promptAndGet(prompt)
  print prompt
  res = readline.chomp
  throw :quitRequested if res == "!"
  return res
end
 
catch :quitRequested do
  name = promptAndGet("Name: ")
  age = promptAndGet("Age: ")
  sex = promptAndGet("Sex: ")
  # ..
  # 处理信息
end
promptAndGet("Name:")

Name: Ruby on Rails
Age: 3
Sex: !
Name:Just Ruby

class FileSaveError < StandardError
  attr_reader :reason
  def initialize(reason)
   @reason = reason
  end
end

File.open(path, "w") do |file|
begin
  # 写出数据 ...
rescue
  # 发生错误
  raise FileSaveError.new($!)
end
end