Truncate string when it is too long

Question

I have two strings:

short_string = "hello world"
long_string = "this is a very long long long .... string" # suppose more than 10000 chars

I want to change the default behavior of print to:

puts short_string
# => "hello world"
puts long_string
# => "this is a very long long....."

The long_string is only partially printed. I tried to change String#to_s, but it didn't work. Does anyone know how to do it like this?

updated

Actually i wanna it works smoothly, that means the following cases also work fine:

> puts very_long_str
> puts [very_long_str]
> puts {:a => very_long_str}

So i think the behavior belongs to String.

Thanks all anyway.

Answer 1

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.

Answer 2

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)"