Ruby Compiler

About the Ruby Compiler

The online Ruby Compiler runs your code with CRuby 4.0, the reference Ruby implementation, compiled to WebAssembly with the standard library included. Test a method, try a new syntax feature or check a Struct, Set or JSON snippet without installing Ruby; the interpreter runs in your browser, so your code stays on your device.

Your code runs in an isolated Web Worker in your browser, so it never leaves your device.

How to use the Ruby Compiler

1. Write or paste Ruby code.
2. Put the lines your program reads with gets or STDIN.read in the stdin box.
3. Click Run. The first run downloads Ruby (about 9 MB); later runs start in under a second.
4. Read the output, or the error with its line number in main.rb.

Example

counts = STDIN.read.downcase.scan(/\w+/).tally
counts.sort_by { |word, n| [-n, word] }.first(3).each do |word, n|
  puts "#{word}: #{n}"
end

the: 3
cat: 1
dog: 1

Common mistakes

• gets returns nil at the end of input. Once the stdin box is used up, gets returns nil, so gets.chomp raises NoMethodError. Use gets&.chomp, or loop with while (line = gets).
• puts, print and p. puts adds a newline and prints arrays one element per line; print adds nothing; p shows the inspected value, with quotes around strings. Use p when you need to see exactly what a value is.
• Requiring a gem. Only the standard library is installed, so require "nokogiri" or "rails" fails with LoadError. Try the logic with standard classes such as Set, Struct, Data and JSON.

Works well with the Ruby Compiler

• Regex Tester: build and test the regular expressions your script uses.
• Python Compiler: compare the same script in Python.
• JSON Formatter: inspect the JSON your program prints.

Frequently asked questions