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The role of regular expressions
Regular expressions (Regular Expression) are a text pattern that includes ordinary characters (such as letters from a to z) and special characters (referred to as "metacharacters"). Regular expressions use a single string to describe and match a series of strings that match a certain syntax rule. Regular expressions are tedious, but they are powerful, and after learning, the application will not only improve efficiency but also bring you a sense of achievement. Many programming languages support string operations using regular expressions.
Common Metacharacters| Code | Description |
|---|---|
| . | Match any character except for the newline character |
| \w | Match any letter or number or underscore |
| \s | Match any whitespace character |
| \d | Match a digit |
| \b | Match the beginning or end of a word |
| ^ | Match the beginning of a string |
| $ | Match the end of a string |
Common Quantifiers
| Code/Syntax | Description |
|---|---|
| * | Match zero or more occurrences |
| + | Match one or more occurrences |
| ? | Match zero or one occurrence |
| {n} | Match exactly n occurrences |
| {n,} | Match at least n occurrences |
| {n,m} | Match between n and m occurrences |
Common Negations
| Code/Syntax | Description |
|---|---|
| \W | Match any character that is not a letter, number, underscore, or Chinese character |
| \S | Match any character that is not a whitespace character |
| \D | Match any character that is not a digit |
| \B | Match a position that is not the beginning or end of a word |
| [^x] | Match any character except x |
| [^aeiou] | Match any character except the letters aeiou |
| Character | Description |
|---|---|
| ^\d+$ | //Matches non-negative integers (positive integers + ) |
| //Matches integer ^\d+(\.\d+)?$ | //Matches non-negative floating-point numbers (positive floating-point numbers + ) |
| ^(([-9]+\.[-9]*[1-9][-9]*)|([-9]*[1-9][-9]*\.[-9]+)|([-9]*[1-9][-9]*))$ | //Matches positive floating-point numbers |
| ^((-\d+(\.\d+)?)|(+(\.+)?))$ | //Matches non-positive floating-point numbers (negative floating-point numbers + ) |
| ^(-(([-9]+\.[-9]*[1-9][-9]*)|([-9]*[1-9][-9]*\.[-9]+)|([-9]*[1-9][-9]*)))$ | //Matches negative floating-point numbers |
| ^(-?\d+)(\.\d+)?$ | //Matches floating-point numbers |
| ^[A-Za-z]+$????????? | //Matches strings composed of 26 English letters |
| ^[A-Z]+$ ??? | //Matches strings composed of 26 uppercase English letters |
| ^[a-z]+$ | //Matches strings composed of 26 lowercase English letters |
| ^[A-Za-z-9]+$ | //Matches strings composed of numbers and 26 English letters |
| ^\w+$ | //Matches strings composed of numbers, 26 English letters, or underscores |
| ^[\w-]+(\.[\w-]+)*@[\w-]+(\.[\w-]+)+$ | //Matches email addresses |
| ^[a-zA-z]+://匹配(\w+(-\w+)*)(\.(\w+(-\w+)*))*(\?\S*)?$ | //Matches URLs |
| [\u4e00-\u9fa5] | Regular expression for matching Chinese characters |
| [^\x00-\xff] | Matches multibyte characters (including Chinese characters) |
| \n[\s| ]*\r | Regular expression for matching empty lines |
| /<(.*)>.*<\/>|<(.*)\/>/ | Regular expression for matching HTML tags |
| (^\s*)|(\s*$) | Regular expression for matching leading and trailing spaces |
| \w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)* | Regular expression for matching Email addresses |
| ^[a-zA-z]+://(\w+(-\w+)*)(\.(\w+(-\w+)*))*(\?\S*)?$ | Regular expression for matching website URLs |
| ^[a-zA-Z][a-zA-Z-9_]{4,15}$ | Matches whether the account is legal (starts with a letter, allows 5-16 bytes, allows letters, numbers, and underscores) |
| (\d{3}-|\d{4}-)?(\d{8}|\d{7})? | Matches domestic phone numbers |
| ^[1-9]*[1-9][-9]*$ | Matches Tencent QQ numbers |
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