Regular Expression learning and collation

Regular Expression learning and collation

/: It is a delimiters. The characters to be matched are generally placed in the delimiters;

2. Common metacharacters

1) +: appears once or multiple times

2) *: zero or multiple occurrences

3 )? : Zero or one occurrence

3. Qualifier

1) character 1 character 2 {n} indicates the matching result of character 2 appearing n times in a row

Character 1 character 2 {n,} indicates the matching result of character 2 that appears n times or more times consecutively

(Character 1 character 2) {n} indicates the matching result of Character 1 character 2 appearing n times in a row

(Character 1 character 2) {n,} indicates the matching result of Character 1 character 2 appearing n times or more times consecutively

Character 1 character 2 {n, m} indicates the matching result between n and m consecutive occurrences of character 2

Example:Text to be matched abcabccabbcabccc

Abc {1} indicates that abcabccabbcabccc occurs once in c.

Abc {2} indicates that c appears twice abcabccabbcabccc

Abc {1,} indicates that c appears once or more abcabccabbcabccc

(Abc) {1,} indicates that abc appears once or more abcabccabbcabccc

4. Special and important metacharacters

. Used to match any character except line breaks

\ S is used to match spaces (lower case)

\ S is used to match content other than spaces (uppercase)

\ D is used to match numbers

\ D is used to match non-Numbers

\ W is used to match letters, numbers, or underscores

\ W is used to match all characters that do not match \ w.

 

5. Positioning Operator

1) ^: starting with the target string

1) $: End of the target string

Example:

The name must start with an 11-digit number: /^ 1 [3 | 4 | 5 | 8] [0-9] \ d {8} $ // 13, 14, 15, 18, the last eight digits are allowed between 0-9.

Determination of numbers within the range of 1000-9999: ^ ([1-9] \ d {3}) $

Number judgment within the range of 2000-2077: ^ 20 ([0-6] \ d | 7 [0-7]) $ // You must note that there are ten digits: 77 can be split into two parts: 0-9 for a single digit in the case of 10-6; 0-7 for a single digit in the case of 10-7.

^ Indicates that the row input starts matching;

$ Indicates the end MATCH mode of the input. The number indicates the original meaning, and the number indicates the number of digits;

\ D represents a digit in 0-9;

| Yes or indicates the selection condition;

() Is a group. If the regular expression is not a group, it is necessary to separate the regular expression into several small regular expressions.