Regular expression introduction and some syntax

Simple translation of characters

Symbol	meaning
\n	Represents a newline character
\t	For tab
\\	representative \ In itself
\^,\$,\(,\),\{,\},\?,\+,\*,|,\[,\]	Match the symbols themselves

Standard character set

Can and Multiple characters Matching expression
Be case sensitive , Capital letters mean the opposite

Symbol	meaning
\d	Any number ,0~9 Any one of
\D	The digital
\w	Any alphanumeric or underscore ,A-Z,a-z,0~9,_
\W	Any character except alphanumeric underscores
\s	Including Spaces 、 tabs 、 Any one of white space characters such as line feed
\S	Except for the space 、 tabs 、 Any character other than the newline character
.	The decimal point can match any character , But it doesn't match the newline character , If you want to match, include \n All the characters in , It's usually used [\s\S]

Custom character set

[] Square brackets match ： Can match any character in the formula bracket

expression	Matching character
[[email protected]]	matching a perhaps b perhaps @ perhaps 5
^ab]	Match except a,b Any character other than
[f-k]	matching f To k Any character between , Include f and k
[^A-F0-3]	Match except A ~ F,0 ~ 3 Any character other than

• stay [ ] in ^ It means to take an objection .
• Special symbols for regular expressions , Enclosed in square brackets , Is to go to the special significance , except ^ and - outside .
• Standard character set , Except that the decimal point in brackets will lose its special meaning , Others don't . [\dab], Match numbers or a,b

quantifiers

A special symbol that modifies the number of matches

expression	meaning
{n}	The expression repeats n Time , Include n
{m,n}	The expression repeats at least m Time , Repeat at most n Time , Include m and n
{m,}	The expression repeats at least m Time , Include m
?	Match expression 0 Time or 1 Time , amount to {0,1}
+	The expression appears at least once , amount to {1,}
*	The expression does not appear or occurs any time , amount to {0,}

• Greedy mode ： The more characters you match, the better , Default . For example, if the following figure is written as c{2,6}, It will match one cccccc.
• Non greedy model ： Is to add a after the quantifier ？ Number . Or the picture below , It's written in c{2,6}?, It will match to 3 individual cc

If it's continuous 6 individual c, Use expressions c{2,3}, Will match to the 2 individual ccc, This is because it matches the first one ccc Time will Recount .

Character boundary

Symbol	meaning
^	What to start with
$	To what end
\b	The left and right boundaries are not all \w , That is, there are not all letters on the left and right , Numbers , Underline

Regular matching patterns

• Ignore case mode
• One way mode ： The entire text is treated as a string , There is only one beginning , An end .
• Multi line mode ： Each line is a string , There's a beginning and an end .

Selector or grouping

expression	effect
|	Between left and right expressions or Relationship , Match left , Or on the right
()	Capture group 1. At the time of being decorated with matching times , Expressions in parentheses can be decorated as a whole .2. Time to get the matching result , The expression in parentheses matches The content can be obtained separately

backreferences ： Each pair of () A number will be assigned , Use () Capture of from... According to the left parenthesis 1 Start AutoNumber .
By reverse reference , You can reference strings that have been captured by grouping , Here's the picture ： The expression in parentheses means that two letters are matched , hinder \1 Said to () References to the contents of , namely （） Match to go,\1 Quote again go, At this time, what this regularization needs is gogo

Assertion

• Match only subexpressions , The matching content is not included in the matching result
• This position should meet certain conditions

expression	meaning
(?=exp)	Assert where it appears The back can be Match to expression exp
(?<=exp)	Assert where it appears Front can Match to expression exp
(?!exp)	Assert where it appears Not in the back Match to expression exp
(?<!exp)	Assert where it appears Not in front Match to expression exp

for example ： Assert that you can match with ing The characters of