Everyday Scripting with Ruby 讀書筆記(1)

[size=small]---
第一個腳本：比較文件清單
A First Script: Comparing File Inventories
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#---
# 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  # 註釋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)  # 註釋⑥
end

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

def inventory_from(filename)
  inventory = File.open(filename)
  downcased = inventory.collect do | line |  # 註釋③
    line.downcase
  end
  downcased.reject do | line |  # 註釋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__  # 註釋①
  check_usage 
  compare_inventory_files(ARGV[0], ARGV[1]) 
end

[color=indigo][b]① $0表示在命令行裏出現的運行腳本的名字, __FILE__表示腳本的名字, 如果是在命令行裏運行的腳本則執行,否則什麼也不做..[/b][/color]
irb(main):001:0> __FILE__
=> "(irb)"
irb(main):002:0> $0
=> "D:/ruby/bin/fxri.rbw"

[color=indigo][b]② unless意爲"除非", 相當於if not..[/b][/color]
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

[color=indigo][b]③ 迭代器collect: 收集代碼塊每次執行的值, 然後放入一個新的數組作爲返回值..[/b][/color]
irb(main):019:0> [1, 2, 3].collect do | ele |
irb(main):020:1* ele * 2
irb(main):021:1> end
=> [2, 4, 6]

[color=indigo][b]④ 迭代器reject: 過濾代碼塊返回爲真的所有元素, 然後放入一個新的數組作爲返回值..[/b][/color]
irb(main):022:0> [1, 2, 3].reject do | ele |
irb(main):023:1* ele == 2
irb(main):024:1> end
=> [1, 3]

[color=indigo][b]⑤ 迭代器any: 數組中任意一個元素使得附帶的代碼塊返回true, 則返回true..[/b][/color]
irb(main):028:0> [1, 2, 3].any? do | ele |
irb(main):029:1* ele > 2
irb(main):030:1> end
=> true

[color=indigo][b]⑥ chomp用來去掉"\n"字符..[/b][/color]
irb(main):031:0> "end\n".chomp
=> "end"