Regular expression Basics

 Regular expressions describe a pattern of string matching , Also known as regular expressions 



 Do these four things with strings  ：   Replace | Division | matching | extract     Preferred regular 



\d	 An arbitrary number 	0~9

\D	 A non number 	 except 0~9

\w	 A letter 	a~z|A~Z|0~9

\W	 A non letter 

\s	 A space 

\S	 A non space 

[]	 Character selector     Match only one “ character ”  [a-c]:a To c Any character between  [ac]：a and c Any character between 

{}	 Range modifier ( Modify how many times the previous symbol appears )	\d{1,2}： Most appear 2 individual , At least a 1 individual 

()	 String selector 	 grouping 	(com|org)

+         Modifier ( The last symbol before the modifier appears at least 1 The maximum number of occurrences is infinite )

*         Modifier ( The last symbol before the modifier appears at least 0 The maximum number of occurrences is infinite )

? Modifier ( The last symbol before the modifier appears at least 0 Most times 1 Time ) If ? Write after modifier , Represents using non greedy mode

^ If used in [^] Take the opposite Single use represents matching from left to right

$ Using alone means matching from right to left

. Match all characters

\ Escape character ( Require regular expressions to contain regular special characters )

^()$ Boundary delimiter ( A complete string match is required ) ^(hello)$

Three modes

• Greedy mode
• Non greedy model use ？ modification
• Exclusive mode