Ruby字符串处理函数

1.返回字符串的长度

str.length => integer

2.判断字符串中是否包含另一个串

str.include? other_str #true or false

"hello".include? "lo" #=> true

"hello".include? "ol" #=> false

"hello".include? ?h #=> true

3.字符串插入:

str.insert(index, other_str) #str

"abcd".insert(0, 'X') #=> "Xabcd"

"abcd".insert(3, 'X') #=> "abcXd"

"abcd".insert(4, 'X') #=> "abcdX"

"abcd".insert(-3, 'X') #=> "abXcd"

"abcd".insert(-1, 'X') #=> "abcdX"

4.字符串分隔,默认分隔符为空格

str.split(pattern=$;, [limit]) # anArray

" now's the time".split #=> ["now's", "the", "time"]

"1, 2.34,56, 7".split(%r{,\s*}) #=> ["1", "2.34", "56", "7"]

"hello".split(//) #=> ["h", "e", "l", "l", "o"]

"hello".split(//, 3) #=> ["h", "e", "llo"]

"hi mom".split(%r{\s*}) #=> ["h", "i", "m", "o", "m"]

"mellow yellow".split("ello") #=> ["m", "w y", "w"]

"1,2,,3,4,,".split(',') #=> ["1", "2", "", "3", "4"]

"1,2,,3,4,,".split(',', 4) #=> ["1", "2", "", "3,4,,"]

也可以指定切分符：

"apples, pears, and peaches".split(", ") # ["apples", "pears", "and peaches"]

"lions and tigers and bears".split(/ and /) # ["lions", "tigers", "bears"]

splite方法的第二个参数用来限制切分的返回结果个数，具体效果规则如下：

1.如果省略这个参数,则切分结果中末尾为null的结果将被压缩掉

2.如果是正数，则结果按照指定的限制数量进行切分，尾部的null结果也将会保留做为结果

3.如果是负数，则切分结果数量无限制，并且保留尾部的null结果。

例如：

str = "alpha,beta,gamma,,"

list1 = str.split(",") # ["alpha","beta","gamma"]

list2 = str.split(",",2) # ["alpha", "beta,gamma,,"]

list3 = str.split(",",4) # ["alpha", "beta", "gamma", ","]

list4 = str.split(",",8) # ["alpha", "beta", "gamma", "", ""]

list5 = str.split(",",-1) # ["alpha", "beta", "gamma", "", ""]

5、格式化字符串

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Ruby的字符串格式话沿用了C的格式，在C中可用于sprintf或printf的格式话字符在Ruby中同样适用：

name = "Bob"

age = 28

str = sprintf("Hi, %s... I see you're %d years old.", name, age)

String类有个%方法，可以方面的做格式化的工作，它接受任何类型的单个值或一个数组：

str = "%-20s %3d" % [name,age]

上面这个和下面这个式子是等效的

str = sprintf("%-20s %3d", name, age)

我们还可以使用ljust,rjust,center方法来格式化我们的字符串：

str = "Moby-Dick"

s1 = str.ljust(13) #"Moby-Dick "

s2 = str.center(13) #" Moby-Dick "

s3 = str.rjust(13) #" Moby-Dick"

6、控制字符串的大小写

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Ruby的String类提供了一组丰富的方法来控制大小写：

s = "Hello,World"

s1 = s.downcase #"hello,world"

s2 = s.upcase #"HELLO,WORLD"

capitalize方法把字符串第一个字符变大写，其余都是小写：

s3 = s.capitalize #"Hello,world"

swapcase则是把字符串中的每个字符的大小写转换一下(原来大写的都小写，反之亦然)：

s = "HELLO,world"

s1 = s.swapcase #"hello,WORLD"

这些方法都有相应的in-place方法

(upcase!,downcase!,capitalize!,swapcase!)

虽然，Ruby没有提供内置的判断字符是否是大小写的方法，但是，这不是问题，我们可以通过正则表达式来完成这一点:

if string =~ /[a-z]/

puts "string contains lowercase charcters"

end

if string =~ /[A-Z]/

puts "string contains uppercase charcters"

end

if string =~ /[A-Z]/ and string =~ /a-z/

puts "string contains mixed case"

end

if string[0..0] =~ /[A-Z]/

puts "string starts with a capital letter"

end

字符串的子串

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Ruby提供了多种访问操作字符串子串的方式，我们可以来看一下：

1.如果给出一组数字，则第一个数字代表取字符串的偏移位置，第二个数字表示

取的长度：

str = "Humpty Dumpty"

sub1 = str[7,4] # "Dump"

sub2 = str[7,99] # "Dumpty" (超过的长度按实际长度来取)

sub3 = str[10,-4] # nil (长度为负数了)

记住，上面的形式，很多从别的语言转过来的ruby初学者会认为给出的两个数字是子串的开始和结束位置的偏移，这是错误的，务必记住。

给出的偏移是负数也是可以的,这样，位置将从字符串末尾开始计算：

str1 = "Alice"

sub1 = str1[-3,3] # "ice"

str2 = "Through the Looking-Glass"

sub3 = str2[-13,4] # "Look"

我们也可以给出一个Range来取子串：

str = "Winston Churchill"

sub1 = str[8..13] # "Church"

sub2 = str[-4..-1] # "hill"

sub3 = str[-1..-4] # nil

sub4 = str[25..30] # nil

强大的是，正则表达式在这个时候也充分发挥着作用：

str = "Alistair Cooke"

sub1 = str[/l..t/] # "list"

sub2 = str[/s.*r/] # "stair"

sub3 = str[/foo/] # nil

如果给出的是一个字符串，则如果目标字符串中含有这个给出的字符串，则返回这个给出的字符串，否则返回nil：

str = "theater"

sub1 = str["heat"] # "heat"

sub2 = str["eat"] # "eat"

sub3 = str["ate"] # "ate"

sub4 = str["beat"] # nil

sub5 = str["cheat"] # nil

如果给出的是一个数字，则返回的是该数字对应索引处字符的ASCII码：

str = "Aaron Burr"

ch1 = str[0] # 65

ch1 = str[1] # 97

ch3 = str[99] # nil

同样，我们不仅可以通过上面的方式访问子串，还可以来向字符串设置内容：

str1 = "Humpty Dumpty"

str1[7,4] = "Moriar" # "Humpty Moriarty"

str2 = "Alice"

str2[-3,3] = "exandra" # "Alexandra"

str3 = "Through the Looking-Glass"

str3[-13,13] = "Mirror" # "Through the Mirror"

str4 = "Winston Churchill"

str4[8..13] = "H" # "Winston Hill"

str5 = "Alistair Cooke"

str5[/e$/] ="ie Monster" # "Alistair Cookie Monster"

str6 = "theater"

str6["er"] = "re" # "theatre"

str7 = "Aaron Burr"

str7[0] = 66 # "Baron Burr"