Ruby Cheatsheet

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cheatsheet ruby

This post contains many useful snippets for me when writing Ruby scripts. I will keep updating this note in the future.

🏷 About File

Absolute Path

__dir__ returns the current path.

File.join(__dir__, file_name_no_path )

Read / Write a file

Read the content of file_name to buffer

buffer = file_name )

Write content to file_name. File will be created when it does not exist. file_name , "w") { |f| f.write( content ) }

🏷 About String

String template

To create a multiline string template:

template = <<-EOCONTENT

String Interpolation

str = "This is a string with #{variable_name}."

Trim a String

"    Hello James ".strip  #=> "Hello James"

Null Or Empty

str.nil? ? "null" : "not_null"
str.empty? ? "empty" : "not_empty"

Titlecase / UPPERCASE / lowercase / Capitalize

All returns a new copy. Examples from this answer in StackOverflow.

"hello James".titleize    #=> "Hello James"
"hello James".upcase      #=> "HELLO JAMES"
"hello James".downcase    #=> "hello james"
"hello James".capitalize  #=> "Hello james"

Note: Alter the original string by adding ! right after the method.

"hello James".downcase!

🏷 About Input

Console Input

Ask a question and wait for user input:

print "Your question: "
user_input = gets

(you may need to strip the user_input to ger rid of a tailing newline.)

🏷 About Regex

Test a ruby regex:

Named regex capturing group


  1. Prepare the regex: ^(\w+)(Query|Command)$.
  2. Add ?<named_group> at the beginning inside that capturing group.
  3. Do the regex match()
  4. Retrieve the named group: [:named_group]
## name: SomeStuffQuery ; result: SomeStuff
result = /^(?<named_group>\w+)(Query|Command)$/.match(name)[:named_group]

If your regex is valid, you should be able to see the captured group and related content:


🏷 About Bundler and Gemfile

Bundler helps you to manage gem denendencies in your project.

Install bundler

gem install bundler
bundler -v

Setup and restore dependencies

Create a Gemfile:

source ''
gem 'dotenv', '~> 2.7', '>= 2.7.5'
gem "mustache", "~> 1.0"


bundle # may requires sudo


To install gems at a relative path e.g. at the lib folder:

bundle install --path=./lib

a .bundle folder will be generated, together with your Gemfile.lock.

Check the info of a installed gem

❯ bundle info ruby_http_client
  * ruby_http_client (3.5.1)
        Summary: A simple REST client
        Path: ~/git/my-folder/lib/ruby/2.6.0/gems/ruby_http_client-3.5.1

(cover image from this dribble)