Dotenv in 7 lines of Ruby or Crystal

dotenv.cr

%w[.env .env.local].each do |file|
  File.read_lines(file).each do |line|
    next if line.starts_with? '#'
    key, value = line.strip.split "=", 2
    ENV[key] = value
  end if File.exists? file
end

dotenv.rb

%w[.env .env.local].each do |file|
  File.readlines(file).each do |line|
    next if line.start_with? "#" # optional
    key, value = line.split "=", 2
    value = value.chomp
    value = value[0..-1] if ['\'', '"'].include? value.chars.first # optional
    value = value[1...-1] if ['\'', '"'].include? value.chars.last # optional
    value = value.gsub '\n', "\n" # optional
    ENV[key] ||= value
  end if File.exists? file
end

You could strip " and ' and convert \n to actual newlines by putting this after the split line:

value = value[0..-1] if ['\'', '"'].includes? value.chars.first
value = value[1...-1] if ['\'', '"'].includes? value.chars.last
value = value.gsub '\n', "\n"

Edit: Added to Ruby version above.

The dotenv gem is 269 lines of code (counting bin and lib only).