Shows a nice screensaver on the terminal with Ruby Curses.

pipes.rb

#!/usr/bin/env ruby
#
# pipes.rb: Displays a nice animation on the terminal,
#           based on an old screensaver.
#
# If you want to see some action, scroll to the bottom.
# The main code is between "begin" and "end".
#
# This code uses Ruby and it's Curses module to display
# characters on the terminal.
#
# I've tried to keep the code clean but it's a mess by
# now. Hey, I was excited when coding, don't blame me.
#
# This code is DEFINITELY not Rubyish. Looks like a messed
# up C/C++ cousing. Maybe that creepy uncle who shows up
# at birthday parties.

require 'curses' # Awesome terminal-handling library

# Since Ruby doesn't natively supports "enums", I've
# used a lot of labels (those things with ':')
# If you find a better one, please tell me (eu@alexdantas.net)
:direction_left
:direction_right
:direction_up
:direction_down

# Represents a single pipe, that will scroll around the
# screen, leaving a colourful trail behind.
class Pipe

  # It's public components.
  attr_reader :x, :y, :behaviour

  # All possible colors that a pipe can have.
  Colors = {
    :black   => 1,
    :white   => 2,
    :red     => 3,
    :yellow  => 4,
    :magenta => 5,
    :blue    => 6,
    :green   => 7,
    :cyan    => 8
  }.freeze

  # The possible ways a pipe can behave.
  # Nice little feature, right?
  Behaviour = [:dumb,  # Randomly decide where to go
               :line,  # Keep making long lines
               :curvy] # Make a lot of curves

  # Constructor, creates a pipe.
  def initialize(x, y, behaviour = :dumb, color = Colors[:cyan])
    @x = x
    @y = y
    @appearance = '-'
    @previous_dir = :direction_right
    @current_dir = :direction_right
    @color = Curses::color_pair color
    @behaviour = behaviour
  end

  # Shows the pipe on the screen.
  # This is VERY UGLY, DAMn.
  def print

    # If we're changing direction it's best to use '+' instead
    # of '-' or '|'
    if @current_dir == :direction_right or @current_dir == :direction_left
      if (@previous_dir == :direction_up or @previous_dir == :direction_down)
        @appearance = '+'
      else
        @appearance = '-'
      end

    elsif @current_dir == :direction_up or @current_dir == :direction_down
      if (@previous_dir == :direction_left or @previous_dir == :direction_right)
        @appearance = '+'
      else
        @appearance = '|'
      end
    end

    Curses::setpos(@y, @x)
    Curses::attrset @color
    Curses::addstr @appearance
    Curses::refresh
  end

  # Refreshes the pipe's direction.
  # If `change_direction` is true, forces the pipe to
  # do it.
  # If not, it will keep on it's current way.
  def refresh_direction(change_direction)

    dir = @current_dir

    if change_direction
      begin
        # Getting a random direction
        result = Random.new.rand(1..4)

        if    result == 1; dir = :direction_left
        elsif result == 2; dir = :direction_up
        elsif result == 3; dir = :direction_right
        else               dir = :direction_down
        end
      end while not is_valid_movement? dir
    end

    @previous_dir = @current_dir
    @current_dir = dir
  end

  # Tells if we can move the cursor to the next direction.
  # Invalid movements will be returning 180o.
  def is_valid_movement? dir
    if (@current_dir == :direction_right and dir == :direction_left)  or
       (@current_dir == :direction_left  and dir == :direction_right) or
       (@current_dir == :direction_up    and dir == :direction_down)  or
       (@current_dir == :direction_down  and dir == :direction_up)
       return false
    else
      return true
    end
  end

  # Actually steps the terminal a position on the screen,
  # based on it's internal directions.
  def move
    if    @current_dir == :direction_right; @x += 1
    elsif @current_dir == :direction_left;  @x -= 1
    elsif @current_dir == :direction_up;    @y -= 1
    elsif @current_dir == :direction_down;  @y += 1
    end

    out_of_screen = false

    if @x < 0
      @x = Curses::cols - 1
      out_of_screen = true
    elsif @x > Curses::cols - 1
      @x = 0
      out_of_screen = true
    end

    if @y < 0
      @y = Curses::lines - 1
      out_of_screen = true
    elsif @y > Curses::lines - 1
      @y = 0
      out_of_screen = true
    end

    self.change_color if out_of_screen
  end

  # Randomly changes the pipe's color.
  def change_color
    result = Random.new.rand(Colors[:red]..Colors[:cyan]) # first..last
    @color = Curses::color_pair result

    # Randomly choosing between normal and bold
    @color = @color | Curses::A_BOLD if random_bool
  end

  # Updates all the pipe's internal stuff.
  def update
    if @behaviour == :dumb
      if random_bool
        self.refresh_direction true
      else
        self.refresh_direction false
      end

    elsif @behaviour == :line
      if random_bool_with_chance 0.2
        self.refresh_direction true
      else
        self.refresh_direction false
      end

    elsif @behaviour == :curvy
      if random_bool_with_chance 0.8
        self.refresh_direction true
      else
        self.refresh_direction false
      end
    end

    self.print
    self.move
  end
end

# Initializes the curses engine.
# ugly function is ugly D:
def curses_init timeout
  Curses::init_screen
  Curses::start_color
  Curses::init_pair(Pipe::Colors[:black],   Curses::COLOR_BLACK,   Curses::COLOR_BLACK)
  Curses::init_pair(Pipe::Colors[:white],   Curses::COLOR_WHITE,   Curses::COLOR_BLACK)
  Curses::init_pair(Pipe::Colors[:red],     Curses::COLOR_RED,     Curses::COLOR_BLACK)
  Curses::init_pair(Pipe::Colors[:yellow],  Curses::COLOR_YELLOW,  Curses::COLOR_BLACK)
  Curses::init_pair(Pipe::Colors[:magenta], Curses::COLOR_MAGENTA, Curses::COLOR_BLACK)
  Curses::init_pair(Pipe::Colors[:blue],    Curses::COLOR_BLUE,    Curses::COLOR_BLACK)
  Curses::init_pair(Pipe::Colors[:green],   Curses::COLOR_GREEN,   Curses::COLOR_BLACK)
  Curses::init_pair(Pipe::Colors[:cyan],    Curses::COLOR_CYAN,    Curses::COLOR_BLACK)
  Curses::curs_set 0
  Curses::noecho
  Curses::nonl
  Curses::timeout = timeout
  Curses::refresh
end

# Returns randomly 'true' or 'false'.
def random_bool
  result = Random.new.rand(1..10)

  if (result % 2) == 0 # is even
    return true
  else
    return false
  end
end

# Returns 'true' or 'false' with a probability of 'chance'
def random_bool_with_chance chance
  result = Random.new.rand(1..100)

  return true if (result <= (chance*100))
  return false
end

# Here's the main function!
#                  _        _  __
#                 (_)      /   \ \
#  _ __ ___   __ _ _ _ __ | |   | |
# | '_ ` _ \ / _` | | '_ \| |   | |
# | | | | | | (_| | | | | | |   | |
# |_| |_| |_|\__,_|_|_| |_| |   | |
#                          \_  /_/
begin
  timeout = 50 # default delay in miliseconds

  curses_init timeout

  pipes = [Pipe.new(Curses::cols/2, Curses::lines/2, :dumb,  Pipe::Colors[:cyan]),
           Pipe.new(Curses::cols/4, Curses::lines/8, :line,  Pipe::Colors[:red]),
           Pipe.new(Curses::cols/8, Curses::lines/4, :curvy, Pipe::Colors[:magenta])]

  while true
    # Updating all pipes
    for i in 0..(pipes.size-1)
      pipes[i].update
    end

    # This is where the timeout delay happens.
    case Curses::getch

    when 'q', 'Q' # quit
      break

    when 'a', 'A' # faster!
      timeout -= 10
      timeout = 10 if timeout < 10
      Curses::timeout = timeout

    when 's', 'S' # slower!
      timeout += 10
      timeout = 50 if timeout > 50
      Curses::timeout = timeout

    when 'c', 'C' # clear
      Curses::clear
      Curses::refresh
    end
  end

  exit 0
end