hilong -- A simply utility to show character counts for each line of input and highlight lines longer than 80 characters.

hilong.rb

#!/usr/bin/env ruby

# A simply utility to show character counts for each line of input and
# highlight lines longer than 80 characters.
#
# Written as an example for http://jstorimer.com/2011/12/12/writing-ruby-scripts-that-respect-pipelines.html
#
# Examples:
#
# $ hilong Gemfile
# $ hilong Gemfile | more
# $ hilong Gemfile > output.txt
# $ hilong Gemfile Gemfile.lock
# $ cat Gemfile* | hilong
# $ cat Gemfile | hilong - Gemfile.lock
#
# Install:
# $ curl https://raw.github.com/gist/1465437/gistfile1.rb > ~/bin/hilong
# $ chmod +x ~/bin/hilong

# escaped bash color codes
red = "\e[31m"
reset_color = "\e[0m"

maximum_line_length = 80
colorized_output = true

require 'optparse'
OptionParser.new do |options|
  # This banner is the first line of your help documentation.
  options.set_banner "Usage: hilong [options] [files]\n" \
    "Show character count for each line of input and highlight long lines."

  # Separator just adds a new line with the specified text.
  options.separator ""
  options.separator "Specific options:"

  options.on("--no-color", "Disable colorized output") do |color|
    colorized_output = color
  end

  options.on("-m", "--max NUM", Integer, "Maximum line length") do |max|
    maximum_line_length = max
  end

  options.on_tail("-h", "--help", "You're looking at it!") do
    $stderr.puts options
    exit 1
  end
end.parse!

# Keep reading lines of input as long as they're coming.
while input = ARGF.gets
  input.each_line do |line|
    # Construct a string that begins with the length of this line
    # and ends with the content. The trailing newline is #chop'ped 
    # off of the content so we can control where the newline occurs.
    # The string are joined with a tab character so that indentation
    # is preserved.
    output_line = [line.size, line.chop].join("\t")

    # If the line is long and our $stdout is not being piped then we'll
    # colorize this line.
    if colorized_output && line.size > maximum_line_length
      # Turn the output to red starting at the first character.
      output_line.insert(0, red)
      # Reset the text color back to what it was at the end of the
      # line.
      output_line.insert(-1, reset_color)
    end

    begin
      $stdout.puts output_line
    rescue Errno::EPIPE
      exit(74)
    end
  end
end

Great example of using pipes with ruby io :)