this is a simple prompt library for ruby. inspired by golang's huh! library's input component. https://github.com/charmbracelet/huh
- Ruby 3.4+
- Bundler
git clone <this-repo>
cd simple-input
bundle installor
gem install simple_inputrequire_relative 'input'
name = Input.new_input
.title('What is your name?')
.prompt('> ')
.validate(:not_empty)
.run
puts "Hello, #{name}!"email = Input.new_input
.title('Enter your email')
.prompt('email> ')
.validate { |val| val.include?('@') ? nil : 'Please enter a valid email' }
.runValidators run in order. The first error found is displayed.
password = Input.new_input
.title('Create a password')
.prompt('password> ')
.validate(:not_empty)
.validate { |val| val.length < 8 ? 'Must be at least 8 characters' : nil }
.runBy default, symbol validators (e.g., :not_empty) resolve against DefaultValidators. You can swap in your own module with with_validators:
module MyValidators
module_function
def email(val)
val.match?(/\A[^@\s]+@[^@\s]+\z/) ? nil : 'Invalid email format'
end
def min_length(val)
val.length >= 3 ? nil : 'Must be at least 3 characters'
end
end
username = Input.new_input
.with_validators(MyValidators)
.validate(:min_length)
.runYou can pass validators in three ways:
| Type | Example |
|---|---|
| Symbol | .validate(:not_empty) - looks up method on the validator provider |
| Proc/Lambda | .validate(-> (val) { val.empty? ? 'required' : nil }) |
| Block | .validate { |val| val.empty? ? 'required' : nil } |
Validators are functions that take a String and return nil (valid) or an error message String.
Use convert_func to transform the input value before it's returned. This is useful for converting strings to integers, floats, arrays, or any other type.
# Convert to integer
age = Input.new_input
.title('How old are you?')
.validate(:not_empty)
.validate { |val| val.match?(/^\d+$/) ? nil : 'Must be a number' }
.convert_func { |val| val.to_i }
.run
puts age.class # => Integer# Convert to array
tags = Input.new_input
.title('Enter tags (comma-separated)')
.convert_func { |val| val.split(',').map(&:strip) }
.run
puts tags.inspect # => ["ruby", "cli", "prompt"]You can pass a converter in two ways:
| Type | Example |
|---|---|
| Proc/Lambda | .convert_func(-> (val) { val.to_i }) |
| Block | .convert_func { |val| val.to_i } |
Converters are functions that take a String and return any type. Validation happens before conversion.
Important: If conversion fails with an exception, an error message will be displayed prompting you to add validation. Always validate input before conversion to prevent errors:
# ❌ Bad - conversion can fail without validation
age = Input.new_input
.convert_func { |val| Integer(val) } # Raises exception on invalid input
.run
# ✅ Good - validate before conversion
age = Input.new_input
.validate(:not_empty)
.validate { |val| val.match?(/^\d+$/) ? nil : 'Must be a number' }
.convert_func { |val| val.to_i }
.run- Ctrl-C - Prints
(canceled)and exits gracefully - Ctrl-D (EOF) - Returns an empty string
| Method | Description |
|---|---|
Input.new_input |
Factory method to create a new Input (.new is private) |
#title(text) |
Set the title displayed above the prompt |
#prompt(text) |
Set the prompt string (default: "> ") |
#validate(validator, &block) |
Add a validator (Symbol, Proc, or block) |
#with_validators(provider) |
Set a custom validator provider module |
#convert_func(converter, &block) |
Set a converter function to transform the input value |
#run |
Start the interactive input loop and return the result |
All methods (except #run) return self for chaining.
Here's a practical example that demonstrates validation, conversion, and dependency injection for testing:
class AreaCalculator
def initialize(reader = $stdin, writer = $stdout)
@reader = reader
@writer = writer
end
# Reusable conversion function
def to_number
->(value) do
if value.to_i.to_s == value
value.to_i
elsif value.to_f.to_s == value
value.to_f
else
raise ArgumentError, "Invalid number: #{value}"
end
end
end
def input_length
Input.new_input
.send(:with_context, @reader, @writer)
.title('What is the length of the room in feet?')
.validate { |value| value.to_i > 0 ? nil : 'Length must be a positive number' }
.convert_func(to_number)
.run
end
def input_width
Input.new_input
.send(:with_context, @reader, @writer)
.title('What is the width of the room in feet?')
.validate { |value| value.to_i > 0 ? nil : 'Width must be a positive number' }
.convert_func(to_number)
.run
end
def calculate_area
length = input_length
width = input_width
area = length * width
@writer.puts "\nYou entered dimensions of #{length} feet by #{width} feet."
@writer.puts "The area is #{area} square feet"
end
endThis example can be tested with RSpec using mocks:
RSpec.describe AreaCalculator do
let(:writer) { double('writer') }
let(:reader) { double('reader') }
subject(:calculator) { AreaCalculator.new(reader, writer) }
before do
allow(writer).to receive(:puts)
allow(writer).to receive(:print)
end
it 'returns integer for valid integer input' do
allow(reader).to receive(:gets).and_return("10\n")
result = calculator.input_length
expect(result).to eq(10)
end
it 'returns float for valid float input' do
allow(reader).to receive(:gets).and_return("10.5\n")
result = calculator.input_length
expect(result).to eq(10.5)
end
endSee examples/area_calculator.rb and examples/area_calculator_spec.rb for the complete implementation.
# Basic usage and validation
ruby examples/basic.rb
# Custom validator providers
ruby examples/custom_validators.rb
# Value conversion (string to int, array, etc.)
ruby examples/convert.rb
# Common validation patterns (email, password, range, choice)
ruby examples/validation_patterns.rb
# Error handling and conversion safety
ruby examples/error_handling.rb
# Area calculator with numeric conversion (practical example)
ruby examples/area_calculator.rbbundle exec rspecThe Input class has a private method with_context(reader, writer) that allows injecting custom IO objects for testing. Since new is also private (enforcing use of Input.new_input), tests use send to access with_context:
def build_input(input_text)
reader = StringIO.new(input_text)
writer = StringIO.new
input = Input.new_input
input.send(:with_context, reader, writer)
[input, writer]
end
# Usage in tests
it 'returns the user input' do
input, = build_input("hello\n")
result = input.run
expect(result).to eq('hello')
end
it 'shows validation errors' do
input, writer = build_input("\nhello\n")
result = input.validate(:not_empty).run
expect(result).to eq('hello')
expect(writer.string).to include('入力してください')
endThis pattern lets you:
- Simulate user input via
StringIOas the reader - Capture all terminal output via
StringIOas the writer - Test the full input loop including validation re-prompting without interactive terminal input
MIT