Ruby 基本语法快速入门

一般语法

每句代码一行，不用分号结尾
代码缩进 不影响 代码含义，一般缩进单位是 2个空格。

注释

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# 这是一个单行注释。

@counter      # 跟踪页面被点击的次数
@siteCounter  # 跟踪所有页面被点击的次数

=begin
这是一个多行注释。
可扩展至任意数量的行。
但 =begin 和 =end 只能出现在第一行和最后一行。 
=end

命名规则

全局变量，a dollar sign ($) 开头
类的实例变量，@ 开头
类的变量，@@ 开头
局部变量、函数参数、方法名，以小写字母或下划线（_）开头
类名、模块名、常量名，大写字母开头

多个单词的实例变量名称，单词之间 用下划线（_）分割。

多个单词的类名，使用驼峰表示法。

函数名后可以跟3种符号： ? ! =

  • 例子 
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    Local Variable:    name fish_and_chips x_axis thx1138 _x _26
Instance Variable:    @name @point_1 @X @_ @plan9
Class Variable:    @@total @@symtab @@N @@x_pos @@SINGLE
Global Variable:    $debug $CUSTOMER $_ $plan9 $Global
Class Name:    String ActiveRecord MyClass
Constant Name:    FEET_PER_MILE DEBUG

变量

变量无需声明

函数

函数定义：

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def say_goodnight(name)
    result = "Good night, " + name
    return result
end

数字

相关的类型： Integer, Fixnum , Bignum, Float

字符串转换为整型： Integer(your-string)

使用数字进行循环：

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3.times { print "X" }
1.upto(5) {|i| print i, " " }
99.downto(95) {|i| print i, " " }
50.step(80, 5) {|i| print i, " " }

字符串 String

单引号和双引号都行： ‘string-literals-in-single-quotation’ “string-literals-in-double-quotation”
还可以用 %q , %Q或%

双引号的字符串，可以包含特殊转义字符串，如 \n #{expression} 。连函数调用都支持： #{name.capitalize}

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    def say_goodnight(name)
        result = "Good night, #{name.capitalize}"
        return result
    end
    puts say_goodnight('uncle')

    produces:
    Good night, Uncle

字符串连接用 +

例如， “hello “ + “world!”

可以通过 [] 访问和设置，字符串中的单个字符

例如：

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person = "Tim"
puts "person is #{person}"
person[0] = 'J'
puts "person is #{person}"

produces:
person is Tim
person is Jim

常用字符串方法

downcase 方法，转换string中字母为小写。
scan(正则表达式)，搜索出字符串中所有match正则表达式的部分，形成数组。

例子：

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def words_from_string(string)
string.downcase.scan(/[\w']+/)
end

p words_from_string("But I didn't inhale, he said (emphatically)")

produces:
["but", "i", "didn't", "inhale", "he", "said", "emphatically"]

start_with? 字符串以什么开头

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puts 'abcdefg'.start_with?('abc')  #=> true

# 可以接受多个参数
'abcdefg'.start_with?( 'xyz', 'opq', 'ab')

检查字符串是否为空？ - string.blank?

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a = nil
b = []
c = ""
c1 = "   "

a.blank? #=> true
b.blank? #=> true
c.blank? #=> true
c1.blank? #=> true

d = "1"
e = ["1"]

d.blank? #=> false
e.blank? #=> false

清除字符串中空格等不可见的格式字符 / strip / strip!

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puts "      \t \n first     ".strip # -> first
puts " \r\n second\n ".strip # -> second
puts "\f\v\r\n\t third".strip # - third

也可以用 delete

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str = " String ".delete(' ')
puts str

str = " \t \r \nString ".delete(" \t\r\n\ ")
puts str

here document

例如：

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string = <<END_OF_STRING
The body of the string is the input lines up to
one starting with the same text that followed the '<<'
END_OF_STRING

Normally, this terminator must start in column one.
However, if you put a minus sign after the << characters, you can indent the terminator:

string = <<-END_OF_STRING
    The body of the string is the input lines up to
    one starting with the same text that followed the '<<'
    END_OF_STRING

String#split 方法

依据分隔符（可以是，正则表达式），对字符串进行分解，提前可用字段。

例子，提取歌曲信息：

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tut_stdtypes/songdata
/jazz/j00132.mp3 | 3:45 | Fats     Waller      | Ain't Misbehavin'
/jazz/j00319.mp3 | 2:58 | Louis    Armstrong   | Wonderful World
/bgrass/bg0732.mp3| 4:09 | Strength in Numbers | Texas Red

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Song = Struct.new(:title, :name, :length)
File.open("songdata") do |song_file|
    songs = []
    song_file.each do |line|
        file, length, name, title = line.chomp.split(/\s*\|\s*/)
        name.squeeze!(" ")
        mins, secs = length.scan(/\d+/)
        songs << Song.new(title, name, mins.to_i*60 + secs.to_i)
    end
    puts songs[1]
end

produces:
#<struct Song title="Wonderful World", name="Louis Armstrong", length=178>

字符串中搜索 include?

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my_string = "abcdefg"
if my_string.include? "cde"
   puts "String includes 'cde'"
end

数组

定义、初始化、引用

如下例：

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a = [ 1, 'cat', 3.14 ] # array with three elements
puts "The first element is #{a[0]}"
# set the third element
a[2] = nil
puts "The array is now #{a.inspect}" # inspect 将 Array 转换为字符串格式：[ 元素1，元素2, ... ]

produces:
The first element is 1
The array is now [1, "cat", nil]

空数组写法

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@books_in_stock = []

检查数组是否为空 any?

向数组中追加元素

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@books_in_stock << BookInStock.new("《Ruby入门》")

元素赋值

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a = [ 1, 3, 5, 7, 9 ] #=> [1, 3, 5, 7, 9]
a[1] = 'bat'          #=> [1, "bat", 5, 7, 9]
a[-3] = 'cat'         #=> [1, "bat", "cat", 7, 9]
a[3] = [ 9, 8 ]       #=> [1, "bat", "cat", [9, 8], 9]
a[6] = 99             #=> [1, "bat", "cat", [9, 8], 9, nil, 99]

数组长度 array.length

提取连续元素

a[index, count] 提取方法，例如：

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a = [ 1, 3, 5, 7, 9 ]
a[1, 3] # => [3, 5, 7]
a[3, 1] # => [7]

a[begin…end] 提取法，例如： 注意 2个点，3个点含义不同

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a = [ 1, 3, 5, 7, 9 ]
a[1..3]  # => [3, 5, 7]
a[1...3] # => [3, 5]
a[3..3]  # =>  [7]

连续元素替换，插入等 []= 操作符的nx功能

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a = [ 1, 3, 5, 7, 9 ]    #=>    [1, 3, 5, 7, 9]
a[2, 2] = 'cat'            #=>    [1, 3, "cat", 9]
a[2, 0] = 'dog'            #=>    [1, 3, "dog", "cat", 9]
a[1, 1] = [ 9, 8, 7 ]   #=>    [1, 9, 8, 7, "dog", "cat", 9]
a[0..3] = []            #=>    ["dog", "cat", 9]
a[5..6] = 99, 98        #=>    ["dog", "cat", 9, nil, nil, 99, 98]

数组当成 栈 使用

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stack = []
stack.push "red"
stack.push "green"
stack.push "blue"
stack                # => ["red", "green", "blue"]

stack.pop    #    =>    "blue"
stack.pop    #    =>    "green"
stack.pop    #    =>    "red"
stack        #    =>    []

数组当成 FIFO队列 使用

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queue = []
queue.push "red"
queue.push "green"
queue.shift # => "red"
queue.shift # => "green"

获取前后连续元素 first & last

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array = [ 1, 2, 3, 4, 5, 6, 7 ]
array.first(4) # => [1, 2, 3, 4]
array.last(4) # => [4, 5, 6, 7]

for 循环遍历数组

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array = [ 1, 2, 3, 4, 5, 6, 7 ]
for num in array
    p num
end

Hash 表

Key-Value键值对数组，Key 必须唯一。

例如：

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inst_section = {
    'cello' =>'string',
    'clarinet' => 'woodwind',
    'drum'=> 'percussion'
}
puts inst_section['cello']  # 引用

初始化值默认nil，例如，访问一个不存在的 key， 其 value 为 nil。
改变 value 的初始化值，例如，默认为0： your-hash = Hash.new(0)

Hash 长度获取，length 方法

使用 Symbol 作为 Key

例子，3种表示方法，都是等价的，第2、3种表示方法，都是使用 Symbol 作为 Key：

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h = { 'dog' => 'canine', 'cat' => 'feline', 'donkey' => 'asinine' }
h = { :dog => 'canine', :cat => 'feline', :donkey => 'asinine' }
h = { dog: 'canine', cat: 'feline', donkey: 'asinine' }

检查Key 是否存在： hash.has_key?(target_key)

Range

Ranges as Sequences
In Ruby, these sequences are created using the .. and … range operators. The two-dot form creates an
inclusive range, and the three-dot form creates a range that excludes the specified high value.

low..high 包含low，high，以及之间的值
low…high 包含low，以及之间的值，不包含high值

Range#to_a 转换为数组

例如：

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(1..10).to_a            # => [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
('bar'..'bat').to_a   # => ["bar", "bas", "bat"]

Range#to_enum 转换为 Enumerator

例如：

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enum = ('bar'..'bat').to_enum
enum.next    # => "bar"
enum.next    # => "bas"

Ranges as Conditions

while line = gets
    puts line if line =~ /start/ .. line =~ /end/
end

Ranges as Intervals

whether some value falls within the interval represented by the range

例子：

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(1..10)       === 5             # => true
(1..10)       === 15            # => false
(1..10)       === 3.14159       # => true
('a'..'j')    === 'c'           # => true
('a'..'j')    === 'z'           # => false

例子：

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car_age = gets.to_f
# let's assume it's 9.5
case car_age
when 0...1
    puts "Mmm.. new car smell"
when 1...3
    puts "Nice and new"
when 3...10
    puts "Reliable but slightly dinged"
when 10...30
    puts "Clunker"
else
    puts "Vintage gem"
end

Symbol 代号

全局的唯一标识符，以冒号开头，例如： :state_ok :state_error

常用来作为hash的key，例如：

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inst_section = {
    :cello =>'string',
    :drum => 'percussion'
}
puts inst_section[:cello]  # 引用

# 简化形式，等价上面的 inst_section
inst_section = {
    cello => 'string',
    drum => 'percussion'
}

程序的控制结构

if

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today = Time.now
if today.saturday?
    puts "Do chores around the house"
elsif today.sunday?
    puts "Relax"
else
    puts "Go to work"
end

produces:
Go to work

if 的变体

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puts "Danger, Will Robinson" if radiation > 3000

while

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while weight < 100 and num_pallets <= 5
    pallet = next_pallet()
    weight += pallet.weight
    num_pallets += 1
end

while 的变体

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square = square*square while square < 1000

for 循环

例子：

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for i in 0...5
    # ...
end

正则表达式 Regular Expressions

/pattern/

=~ 操作符

使用方式：字符串 =~ /pattern/
If the pattern is found in the string,
=~ returns its starting position; otherwise, it returns nil.

例如：

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line = gets
if line =~ /Perl|Python/
    puts "Scripting language mentioned: #{line}"
end

match 方法

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2.3.7  > s = "202206"
 => "202206" 
2.3.7  > m = s.match(%r{(\d{4})(\d{2})})
 => #<MatchData "202206" 1:"2022" 2:"06"> 
2.3.7  > m[0]
 => "202206" 
2.3.7  > m[1]
 => "2022" 
2.3.7  > m[2]
 => "06"

利用 regex 替换

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line = gets

# replace first 'Perl' with 'Ruby'
newline = line.sub( /Perl/, 'Ruby' )

# replace every 'Python' with 'Ruby'
newerline = newline.gsub( /Python/, 'Ruby' )

# You can replace every occurrence of Perl and Python with Ruby using this:
newline = line.gsub( /Perl|Python/ , 'Ruby')

时间

  • 获取时间戳
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require 'date'

p DateTime.now.strftime('%s') # "1384526946" (seconds)
p DateTime.now.strftime('%Q') # "1384526946523" (milliseconds)
  • 从字符串生成 date 对象
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str = "Tue, 10 Aug 2010 01:20:19 +0400"

# Date.parse 会忽略时间
puts Date.parse str

# Time.parse 是日期+时间
puts Time.parse str
  • 从时间生成字符串
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datetime.strftime('%Y-%m-%d %H:%M:%S')