Creating an infinite loop

Question

I'm trying to create an infinite loop, where a block of code will be executed forever.

All loop documentation I have found warns against creating an infinite loop, but no examples of a working one.

If I have a block of code:

{ puts "foo"  
  puts "bar"  
  sleep 300 }

How would I go about running this block forever?

You've tagged this `ruby-on-rails`. If you're trying to create an infinite loop in Rails, you're probably doing something horribly wrong. You can't do that in the same process that is serving your site, or the single thread of execution cannot actually respond to incoming requests. If you want to do something every 300 seconds, you need an asynchronous background job. You should describe your actual problem so we can provide you with real advice - using an infinite loop is a *solution*, not a *problem*. — user229044, Nov 26 '14 at 01:49
Thank you for clarifying. This loop is not being used for rails. I have removed the tag. Thanks for the explanation! — Andrew Walz, Nov 26 '14 at 02:18

score 45 · Accepted Answer · answered Nov 26 '14 at 01:41

45

loop do
  puts 'foo'  
  puts 'bar'  
  sleep 300
end

answered Nov 26 '14 at 01:41

Todd A. Jacobs

81,402
15
141
199

Upvoted for a correct answer, but the best answer is probably still @meagar's in question comments. :) – Amadan Nov 26 '14 at 02:10

vgoff · Answer 2 · 2019-10-10T17:47:11.110

Here are some examples of infinite loops using blocks.

Loop

loop do
  puts "foo"  
  puts "bar"  
  sleep 300
end

While

while true
  puts "foo"  
  puts "bar"  
  sleep 300
end

Until

until false
  puts "foo"  
  puts "bar"  
  sleep 300
end

Lambda

-> { puts "foo" ; puts "bar" ; sleep 300}.call until false

There are a few variations of the lambda as well, using the non-stabby lambda syntax. Also we could use a Proc.

Begin..End

begin
  puts "foo"  
  puts "bar"
  sleep 300
end while true

score 1 · Answer 3 · answered Jan 01 '19 at 01:17

1

I have tried all but with inputs loop only worked as infinty loop till I get a valid input:

loop do
    a = gets.to_i
    if (a >= 2)
        break
    else 
        puts "Invalid Input, Please enter a correct Value >=2: "
    end
end

answered Jan 01 '19 at 01:17

Abdelrahman Farag

389
2
9

Rahul Dess · Answer 4 · 2014-11-26T02:42:50.413

-6

1) While loop:

While 1==1 # As the condition 1 is equal to 1 is true, it always runs.
    puts "foo"  
    puts "bar"  
    sleep 300
   end

2) Recursion :

    def infiniteLoop # Using recursion concept
      puts "foo"
      puts "bar"
      sleep 300
      infiniteLoop #Calling this method again    
    end

EDIT : I thought this would work, but as Gabriel mentioned, we would get SystemStackError.

3) Loop

   loop do
    puts "foo"
    ....
   end

4) Using unless

unless 1 == 2  # Unless 1 is equal to 2 , it keeps running
 puts "foo"
 ...
end

edited Nov 26 '14 at 02:42

answered Nov 26 '14 at 01:55

Rahul Dess

2,397
2
21
42

6

`unless` is not a loop construct, it is a synonym for `if not`. You might have been thinking of `until`, a synonym for `while not`. And while we're on `while`, Ruby is case-sensitive: `While` is an undefined constant, and not a keyword like `while` is; and as a keyword, it does not accept a block, so `while ... do` is a syntax error as well. – Amadan Nov 26 '14 at 02:08
4

The recursion alternative will not work as with each iteration you're adding a level to the stack and eventually a [`SystemStackError`](http://www.ruby-doc.org/core-2.1.5/SystemStackError.html) will be raised. – Gabriel de Oliveira Nov 26 '14 at 02:25

Creating an infinite loop

4 Answers4

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