Everyday Scripting with Ruby 读书笔记(1)

---
第一个脚本：比较文件清单
A First Script: Comparing File Inventories
---

#---
# Excerpted from "Everyday Scripting in Ruby"
# We make no guarantees that this code is fit for any purpose. 
# Visit http://www.pragmaticprogrammer.com/titles/bmsft for more book information.
#---
def check_usage
  unless ARGV.length == 2  # 注释②
    puts "Usage: differences.rb old-inventory new-inventory"
    exit
  end
end

def boring?(line)
  line.chomp.split('/').include?('temp') or
    line.chomp.split('/').include?('recycler')
  end
  
def contains?(line, key)
  line.chomp.split('/').include?(key)  # 注释⑥
end

def boring?(line, boring_words)
  boring_words.any? do | a_boring_word |  # 注释⑤
    contains?(line, a_boring_word)
  end
end

def inventory_from(filename)
  inventory = File.open(filename)
  downcased = inventory.collect do | line |  # 注释③
    line.downcase
  end
  downcased.reject do | line |  # 注释④
    # contains?(line, 'temp') or contains?(line, 'recycler')
    boring?(line, ['temp','recycler'])
  end
end

def compare_inventory_files(old_file, new_file)
  old_inventory = inventory_from(old_file)
  new_inventory = inventory_from(new_file)

  puts "The following files have been added:"
  puts new_inventory - old_inventory

  puts ""
  puts "The following files have been deleted:"
  puts old_inventory - new_inventory
end

if $0 == __FILE__  # 注释①
  check_usage 
  compare_inventory_files(ARGV[0], ARGV[1]) 
end

① $0表示在命令行里出现的运行脚本的名字, __FILE__表示脚本的名字, 如果是在命令行里运行的脚本则执行,否则什么也不做..
irb(main):001:0> __FILE__
=> "(irb)"
irb(main):002:0> $0
=> "D:/ruby/bin/fxri.rbw"

② unless意为"除非", 相当于if not..
irb(main):012:0> def check_unless(x)
irb(main):013:1>   unless x==2
irb(main):014:2>     puts "x does not equal 2"
irb(main):015:2>     end
irb(main):016:1>   end
=> nil
irb(main):017:0> check_unless(2)
=> nil
irb(main):018:0> check_unless(3)
x does not equal 2
=> nil

③ 迭代器collect: 收集代码块每次执行的值, 然后放入一个新的数组作为返回值..
irb(main):019:0> [1, 2, 3].collect do | ele |
irb(main):020:1*   ele * 2
irb(main):021:1>   end
=> [2, 4, 6]

④ 迭代器reject: 过滤代码块返回为真的所有元素, 然后放入一个新的数组作为返回值..
irb(main):022:0> [1, 2, 3].reject do | ele |
irb(main):023:1*   ele == 2
irb(main):024:1>   end
=> [1, 3]

⑤ 迭代器any: 数组中任意一个元素使得附带的代码块返回true, 则返回true..
irb(main):028:0> [1, 2, 3].any? do | ele |
irb(main):029:1*   ele > 2
irb(main):030:1>   end
=> true

⑥ chomp用来去掉"\n"字符..
irb(main):031:0> "end\n".chomp
=> "end"