while conditional [do]
  code
end

#!/usr/bin/ruby
 
$i = 0
$num = 5
 
while $i < $num do
  puts("Inside the loop i = #$i" )
  $i +=1
end

Inside the loop i = 0
Inside the loop i = 1
Inside the loop i = 2
Inside the loop i = 3
Inside the loop i = 4

code while condition
 
OR
 
begin
 code
end while conditional

#!/usr/bin/ruby
 
$i = 0
$num = 5
begin
  puts("Inside the loop i = #$i" )
  $i +=1
end while $i < $num

Inside the loop i = 0
Inside the loop i = 1
Inside the loop i = 2
Inside the loop i = 3
Inside the loop i = 4
Ruby until 语句
until conditional [do]
  code
end

#!/usr/bin/ruby
 
$i = 0
$num = 5
 
until $i > $num do
  puts("Inside the loop i = #$i" )
  $i +=1;
end

Inside the loop i = 0
Inside the loop i = 1
Inside the loop i = 2
Inside the loop i = 3
Inside the loop i = 4
Inside the loop i = 5
Ruby until 修饰符
语法
code until conditional
 
OR
 
begin
  code
end until conditional

#!/usr/bin/ruby
 
$i = 0
$num = 5
begin
  puts("Inside the loop i = #$i" )
  $i +=1;
end until $i > $num

Inside the loop i = 0
Inside the loop i = 1
Inside the loop i = 2
Inside the loop i = 3
Inside the loop i = 4
Inside the loop i = 5

for variable [, variable ...] in expression [do]
  code
end

#!/usr/bin/ruby
 
for i in 0..5
  puts "Value of local variable is #{i}"
end

Value of local variable is 0
Value of local variable is 1
Value of local variable is 2
Value of local variable is 3
Value of local variable is 4
Value of local variable is 5

#!/usr/bin/ruby
 
(0..5).each do |i|
  puts "Value of local variable is #{i}"
end

Value of local variable is 0
Value of local variable is 1
Value of local variable is 2
Value of local variable is 3
Value of local variable is 4
Value of local variable is 5

#!/usr/bin/ruby
 
for i in 0..5
  if i > 2 then
   break
  end
  puts "Value of local variable is #{i}"
end

Value of local variable is 0
Value of local variable is 1
Value of local variable is 2

#!/usr/bin/ruby
 
for i in 0..5
  if i < 2 then
   next
  end
  puts "Value of local variable is #{i}"
end

Value of local variable is 2
Value of local variable is 3
Value of local variable is 4
Value of local variable is 5

#!/usr/bin/ruby
 
for i in 0..5
  if i < 2 then
   puts "Value of local variable is #{i}"
   redo
  end
end

Value of local variable is 0
Value of local variable is 0
............................

begin
  do_something # 抛出的异常
rescue
  # 处理错误
  retry # 重新从 begin 开始
end

for i in 1..5
  retry if some_condition # 重新从 i == 1 开始
end

#!/usr/bin/ruby
 
for i in 1..5
  retry if i > 2
  puts "Value of local variable is #{i}"
end

Value of local variable is 1
Value of local variable is 2
Value of local variable is 1
Value of local variable is 2
Value of local variable is 1
Value of local variable is 2
............................