A simple utility to extract patterns out of input streams

extract.rb

#!/usr/bin/env ruby

# A simple utility to extract patterns out of input streams
#
# Heavily inspired by:
#   http://jstorimer.com/2011/12/12/writing-ruby-scripts-that-respect-pipelines.html
#   https://gist.github.com/jstorimer/1465437
#
# Examples:
#
# $ extract PATTERN Gemfile
# $ extract PATTERN Gemfile | more
# $ extract PATTERN Gemfile > output.txt
# $ extract PATTERN Gemfile Gemfile.lock
# $ cat Gemfile* | extract PATTERN
#
# Install:
# $ curl https://gist.githubusercontent.com/exploid/8dae1d39544fad407924/raw/2d0da9234de179c43d5e3020e6b6272f10ed3d80/extract.rb > ~/bin/extract
# $ chmod +x ~/bin/extract

require 'optparse'

$options = { }

OptionParser.new do |opts|
  opts.banner = "A simple utility to extract patterns out of input streams"
  opts.separator ""
  opts.separator "Usage:"
  opts.separator "  extract PATTERN Gemfile"
  opts.separator "  extract PATTERN Gemfile | more"
  opts.separator "  extract PATTERN Gemfile > output.txt"
  opts.separator "  extract PATTERN Gemfile Gemfile.lock"
  opts.separator "  cat Gemfile* | extract PATTERN"
  opts.separator ""
  opts.separator "Specific options:"

  opts.on("-i", "--ip", "Match IP addresses") do |ip|
    $options[:extract_pattern] = /\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/
  end

  opts.on("-p", "--pattern", String, "PATTERN (Ruby regular expression)") do |pattern|
    $options[:extract_pattern] = pattern
  end

  opts.on("-h", "--help", "help") do |h|
    puts opts
    exit
  end

end.parse!

if $options[:extract_pattern].nil?
  $options[:extract_pattern] = ARGV.shift || ""
end

# Keep reading lines of input as long as they're coming.
while input = ARGF.gets
  input.each_line do |line|
    if $options[:extract_pattern]
      matches = line.scan(Regexp.new($options[:extract_pattern]))

      if matches.any?
        begin
          $stdout.puts matches.join(", ")
        rescue Errno::EPIPE
          exit(74)
        end
      end
    end
  end
end