RubyHow-ToBeginner · 3 min read

How to Use redo in Ruby: Syntax and Examples

In Ruby, redo restarts the current iteration of a loop without checking the loop condition again. It is used inside loops like while, for, or each to repeat the current step immediately.

📐

Syntax

The redo keyword is used inside a loop to restart the current iteration without moving to the next one or re-checking the loop condition.

It can be used in loops such as while, until, for, and each.

Basic syntax:

loop do
  # some code
  redo if condition
end

Here, if condition is true, the loop repeats the current iteration immediately.

ruby

loop do
  puts "Hello"
  redo if false
  break
end

Output

Hello

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Example

This example shows how redo repeats the current loop iteration when a condition is met, without moving forward.

ruby

i = 0
loop do
  i += 1
  puts "Count: #{i}"
  if i == 3
    puts "Redoing iteration when i is 3"
    redo
  end
  break if i >= 5
end

Output

Count: 1 Count: 2 Count: 3 Redoing iteration when i is 3 Count: 3 Redoing iteration when i is 3 Count: 3 Redoing iteration when i is 3 ... (infinite loop)

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Common Pitfalls

Using redo without changing the loop variables or conditions can cause an infinite loop because the same iteration repeats endlessly.

Always ensure that something changes inside the loop before redo is called to avoid this.

ruby

i = 0
loop do
  puts i
  redo if i == 0  # This causes infinite loop because i never changes
  i += 1
  break if i > 2
end

# Correct way:
i = 0
loop do
  puts i
  if i == 0
    i += 1
    redo
  end
  break if i > 2
  i += 1
end

Output

0 0 0 ... (infinite loop) 0 1 2

📊

Quick Reference

Keyword	Description
redo	Restarts the current iteration of a loop without re-checking the condition
break	Exits the loop immediately
next	Skips to the next iteration of the loop
retry (legacy)	Used in older Ruby versions to restart the entire loop (deprecated)

✅

Key Takeaways

Use redo inside loops to repeat the current iteration without re-evaluating the loop condition.

Avoid infinite loops by ensuring loop variables or conditions change before calling redo.

redo works with loops like while, for, and each.

Do not confuse redo with next or break; redo repeats the same iteration.

The retry keyword is deprecated for loops; use redo instead.