This is the fourth day of my participation in the August More text Challenge. For details, see: August More Text Challenge
Regular expression, this thing I am sure will make a lot of people headache a thing, today to liver a liver headache regular expression.
Introduction to Regular Expressions
Regular Expression: A Regular Expression is a logical formula for manipulating strings. It uses predefined characters and their sum to form a “rule string”. The rule string is used to filter strings.
Functions of regular expressions
- Whether the given string conforms to the filtering logic of the regular expression (matching).
- We can use regular expressions to get the specific part (extract) we want from the string.
- Powerful string substitution capability (substitution).
Features of regular expressions
- Flexible, logical and functional.
- Complex control of strings can be achieved quickly and in a very simple manner.
Regular expression syntax
Online test re
Composition of a regular expression
- The common characters ABC, Chinese 123, etc
- Special characters (metacaracters, qualifiers, and brackets) : Characters that have special meanings in a regular expression.
metacharacters
Metacharacters are characters that have special meanings in regular expressions.
| metacharacters | instructions |
|---|---|
| \d | Match the Numbers |
| \D | Matching non-number |
| \w | Matches letters or numbers or underscores _ |
| \W | Matches letters, digits, and underscores |
| \s | Match whitespace (Spaces) |
| \S | Matches non-whitespace characters |
| . | Matches any single character other than the newline (carriage return key) |
qualifiers
A qualifier is a limit on the number of characters that can occur
| qualifiers | instructions |
|---|---|
| n* | Matches any string containing zero or more n’s. n{0,} |
| n+ | Matches any string containing at least one n. n{1,} |
| n? | Matches any string containing zero or one n. {0, 1} |
| n{x} | Matches a string containing x sequences of n. |
| n{x,} | Matches a string that contains at least x sequences of n. |
| n{x,y} | Matches a string that contains at least X sequences and at most y sequences of n. |
| n$ | Matches any string ending in n. |
| ^n | Matches any string that starts with n. |
| Note: |
- When a regular expression is used, the whole string is checked to ensure that the string matches only if it matches completely. Otherwise it doesn’t match.
- For the number limit in curly braces, when matching a string, the previous order is matched first, and the maximum number is matched first. If the maximum number does not meet the requirements, the smaller number is matched.
- If the number limit in curly braces is at least 0, no matching item in the string meets the requirement, and no matching character in the string meets the requirement.
brackets
A bracket represents a string, and the purpose of the bracket is to control the range of a character.
| brackets | instructions |
|---|---|
| [abc] | Finds any character between parentheses. |
| [^abc] | Looks for any character that is not in between square brackets, where ^ has an inverse in brackets. |
| [0-9] | Look for any number from 0 to 9. |
| [a-z] | Looks for any character from small a to lowercase Z. |
| [A-Z] | Finds any character from capital A to capital Z. |
| [A-z] | Find a letter (case and underscore). |
| [[\u4e00-\u9fa5]] | Find a Chinese character. |
In the match, the search is performed from the front to the back according to the [rule]. If there is a global match, the match starts from the next one when there is a match.
Or pattern
Special symbols: regular 1 | 2, regular or. It matches or one of the two sides.
For example: Google, Baidu, Bing; // Matches one of the three strings
Regular: Google | baidu | bing
Grouping pattern
Special symbols: (regular);
Group refers to a small group, grouping is a large group can be divided into several small groups.
For example: control the number of consecutive occurrences of your name, from a minimum of 1 to a maximum of 3
Regular: ^ (Bruce) ${1, 3}
The modifier
- G, global, means global match. Such as:
var reg = /hello/g; - I, ignore, means you can ignore the case of a letter when you match it. Such as:
var reg = /hello/i; - Gi, global matching and ignoring case are used together. Such as:
var reg = /hello/gi;
The regular escape character
Represents a special symbol in a re. To remove the special meaning of.
Js uses regular expressions
Regular expression object
- Create a regular expression object
Var var = new RegExp(" rule "," modifier ") */
var reg = new RegExp('\\d'.'g')
/** Method 2: Syntax: var variable = / regular expression/(recommended) */
var reg = /\d/g;
Copy the code- Detect matches: regular object test(string); Checks whether a string matches a rule. Returns true and false
String object methods related to regular use
- Match (regular object); Gets the substring that matches the re and returns an array.
- Replace (regular object, the contents after the replacement); Replaces the substring of the matched re. Returns the replaced string.
Praise support, hand stay fragrance, and have glory yan, thank you for leaving your footprints.
If you’re interested, leave a comment below with some regular expressions you use frequently