Truncate String When It Is Too Long

First of all, you need a method to truncate a string, either something like:

def truncate(string, max)
  string.length > max ? "#{string[0...max]}..." : string
end

Or by extending String: (it's not recommended to alter core classes, though)

class String
  def truncate(max)
    length > max ? "#{self[0...max]}..." : self
  end
end

Now you can call truncate when printing the string:

puts "short string".truncate
#=> short string

puts "a very, very, very, very long string".truncate
#=> a very, very, very, ...

Or you could just define your own puts:

def puts(string)
  super(string.truncate(20))
end

puts "short string"
#=> short string

puts "a very, very, very, very long string"
#=> a very, very, very, ...

Note that Kernel#puts takes a variable number of arguments, you might want to change your puts method accordingly.

This is how Ruby on Rails does it in their String#truncate method as a monkey-patch:

class String
  def truncate(truncate_at, options = {})
    return dup unless length > truncate_at

    options[:omission] ||= '...'
    length_with_room_for_omission = truncate_at - options[:omission].length
    stop = if options[:separator]
      rindex(options[:separator], length_with_room_for_omission) || 
        length_with_room_for_omission
      else
        length_with_room_for_omission
      end

    "#{self[0...stop]}#{options[:omission]}"
  end
end

Then you can use it like this

'And they found that many people were sleeping better.'.truncate(25, omission: '... (continued)')
# => "And they f... (continued)"

You can write a wrapper around puts that handles truncation for you:

def pleasant(string, length = 32)
  raise 'Pleasant: Length should be greater than 3' unless length > 3

  truncated_string = string.to_s
  if truncated_string.length > length
    truncated_string = truncated_string[0...(length - 3)]
    truncated_string += '...'
  end

  puts truncated_string
  truncated_string
end

Truncate naturally

I want to propose a solution that truncates naturally. I fell in love with the String#truncate method offered by Ruby on Rails. It was already mentioned by @Oto Brglez above. Unfortunately I couldn't rewrite it for pure ruby. So I wrote this function.

def truncate(content, max)    
    if content.length > max
        truncated = ""
        collector = ""
        content = content.split(" ")
        content.each do |word|
            word = word + " " 
            collector << word
            truncated << word if collector.length < max
        end
        truncated = truncated.strip.chomp(",").concat("...")
    else
        truncated = content
    end
    return truncated
end

Example

• Test: I am a sample phrase to show the result of this function.
• NOT: I am a sample phrase to show the result of th...
• BUT: I am a sample phrase to show the result of...

Note: I'm open for improvements because I'm convinced that there is a shorter solution possible.