Common tools - regular expression

1. matches a single character

You can match any single character. (Most can not match newline)

2. Match a set of characters

[] Define a set of characters; 0-9, az one character interval; ^ negated operation.

abc[^0-9]  //abc开头，最后一位不为数字

3. metacharacters

3.1 match whitespace characters

Metacharacters	Explanation
[\b]	Back one character
\f	Page breaks
\n	Newline
\r	Carriage return
\t	Tabs
\ v	Vertical tab

3.2 Matching specific character

Metacharacters	Explanation
\d	Numeric characters, equivalent [0-9]
\D	Non-numeric characters, equivalent [^ 0-9]
\w	+ + Number underline case, equivalent [a-zA-Z0-9_]
\W	Taking a negation of the above, equivalent to [^ a-zA-Z0-9_]
\s	Any blank character, equivalent to [\ f \ n \ t \ v \ r]
\S	To take on non

4. Repeat Match

• + Matches one or more characters
• * Matches zero or more characters
• ? Matches zero or one characters
  + and * are greedy type metacharacter will match the content as much as possible,? Lazy type.

[\w.]+@\w+\.\w+    //匹配邮箱地址
a.+c    //这个就能匹配abcabcabcabc

• {N} n characters matches
• {M, n} m ~ n characters match
• {M,} characters match at least m

The position matching

• \ B matches a word boundary
• \ B matches the position of non-word boundary
• ^ Matches the beginning of a string
• $ Matches the end

^\s*\/\/.*$   //匹配以//开头的注释行

6. subexpression

• () Is defined subexpression
• | The two parts of the left and right as long as there is a match you can

(ab){2,}  //匹配至少两个ab相连
(19|20)\d{2}  //匹配19或者20开头的年份

7. trackback

\ N is a reference to the n-th expression, with reference to the sub-expression matches the same content.

<(h[1-6])>\w*?<\/\1>    //匹配HTML的标题元素<h1>x</h1>

8. Replace

//查找正则表达式
(\d{3})(-)(\d{3})(-)(\d{4})
//替换正则表达式
//在第一个子表达式查找的结果加上 () 
//然后加一个空格
//在第三个和第五个字表达式查找的结果中间加上-进行分隔。
($1) $3-$5

8.1 Case Conversion

Metacharacters	Explanation
\l	The next character to lowercase
\ in	The next character to uppercase
\L	The \ character between L and \ E converting all lowercase
\ In	The \ characters between U and \ E all converted to uppercase
\E	End \ L or \ U

(\w)(\w{2})(\w) //查找正则
$1\U$2\E$3  //将第二个和第三个字符转为大写

9. Find a before and after

• ? = Lookahead, matching text does not appear to match the results, the child must be used in expressions.

.+(?=:)  //匹配网址，返回http而不是http:

• ? <= Look back, matching text does not appear to match the results, the child must be used in expressions.

(?<=\$)[0-9.]+  //匹配金钱数目，返回23.54而不是$23.54

• Negated manipulation!

10. The embedded condition

• Trackback conditions: first determine a sub-expression, if the match is to continue matching subsequent content.

//(\() 匹配一个左括号
//?(1) 当表达式1匹配，则继续后续匹配，这里是匹配右括号
(\()?abc(?(1)\))

• Before and after the search criteria: after finding the forward or backward lookup operation to succeed, it continues to match the subsequent content. Rarely used.