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,,"]

5.字符串替换

str.gsub(pattern, replacement) => new_str
str.gsub(pattern) {|match| block } => new_str
"hello".gsub(/[aeiou]/, '*')  #=> "h*ll*" #将元音替换成*号
"hello".gsub(/([aeiou])/, '<\1>') #=> "h<e>ll<o>"   #将元音加上尖括号,\1表示保留原有字符???
"hello".gsub(/./) {|s| s[0].to_s + ' '}   #=> "104 101 108 108 111 "

字符串替换二:

str.replace(other_str) => str
s = "hello" #=> "hello"
s.replace "world"   #=> "world"

6.字符串删除

str.delete([other_str]+) => new_str
"hello".delete "l","lo"#=> "heo"
"hello".delete "lo"#=> "he"
"hello".delete "aeiou", "^e"   #=> "hell"
"hello".delete "ej-m"  #=> "ho"

7.去掉前和后的空格

str.lstrip => new_str
" hello ".lstrip   #=> "hello "
" hello ".rstrip   #=> " hello"
" hello ".strip #=> "hello"

8.字符串匹配

str.match(pattern) => matchdata or nil

9.字符串反转

str.reverse => new_str
"stressed".reverse   #=> "desserts"

10.去掉重复的字符

str.squeeze([other_str]*) => new_str
"yellow moon".squeeze  #=> "yelow mon" #默认去掉串中所有重复的字符
" now   is the".squeeze(" ") #=> " now is the" #去掉串中重复的空格
"putters shoot balls".squeeze("m-z")   #=> "puters shot balls" #去掉指定范围内的重复字符

11.转化成数字

str.to_i=> str
"12345".to_i #=> 12345

chomp和chop的区别:

chomp:去掉字符串末尾的\n或\r
chop:去掉字符串末尾的最后一个字符,不管是\n\r还是普通字符

"hello".chomp#=> "hello"
"hello\n".chomp  #=> "hello"
"hello\r\n".chomp#=> "hello"
"hello\n\r".chomp#=> "hello\n"
"hello\r".chomp  #=> "hello"
"hello".chomp("llo") #=> "he"

"string\r\n".chop   #=> "string"
"string\n\r".chop   #=> "string\n"
"string\n".chop #=> "string"
"string".chop   #=> "strin"

String#split

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

将一个字符串用分隔符分割成一些子字符串，并返回一个包含这些子字符串的数组。
如果PATTERN部分是一个字符串，那么用它作分割符来分隔，如果PATTERN是一个空格，那么在空格处分割，并且临近的空格被忽略。
如果PATTERN是个正则表达式，那么在匹配PATTERN的地方分割，当PATTERN是长度为0的字符串，那么SPLIT将把字符串分割为单个字符
如果PATTERN被忽略，将用$;来分隔，如果$;没有设置（就是在默认状态），SPLIT将制定空格' '
如果LIMIT参数被忽略，跟踪空段被抑制，如果LIMIT是个正数，那么至多返回LIMIT个字段（如果是1，那么将整个字符串作为一个字段返回），如果是个负数，那么跟踪空段不被抑制。

" now's the time".split #=> ["now's", "the", "time"]
" now's the time".split(' ') #=> ["now's", "the", "time"]
" 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,,"]
"1,2,,3,4,,".split(',', -4) #=> ["1", "2", "", "3", "4", "", ""]

如果包含特殊字符，注意转义

"wo | shi | yi | ge | bing".split(/\s*\|\s*) #竖杠别忘了转义

和String.scan的区别

split中的pattern是分隔符，而scan中的pattern指的是要匹配的东西

"123=342=4234=523421=6424".scan(/\d+/) #=> ["123","342","4234","523421","6424"]

如果匹配项被括起来，那么则会保留分割符，例如： ##

"Three little words".split(/\s+/) #===>["three","little",words"]
"Three little words".split(/(\s+)/) #===>["three"," ","little"," ","words"] 保留了空格