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The role of regular expressions
Regular expression (Regular Expression) is a text pattern that includes ordinary characters (for example, letters between a and z) and special characters (called "metacharacters"). Regular expressions use a single string to describe and match a series of strings that match a certain syntax rule. Regular expressions are cumbersome, but they are powerful. The application after learning them will not only improve your efficiency, but also give you an absolute sense of accomplishment. Many programming languages support the use of regular expressions for string operations.
Commonly used metacharacters| code | illustrate |
|---|---|
| . | Matches any character except newlines |
| \w | Match letters or numbers or underscores |
| \s | Matches any whitespace character |
| \d | Match numbers |
| \b | Match the beginning or end of a word |
| ^ | Matches the beginning of a string |
| $ | Match the end of the string |
Common qualifiers| code/syntax | illustrate |
|---|---|
| * | Repeat zero or more times |
| + | Repeat one or more times |
| ? | Repeat zero or one time |
| {n} | Repeat n times |
| {n,} | Repeat n or more times |
| {n,m} | Repeat n to m times |
Commonly used antonyms| code/syntax | illustrate |
|---|---|
| \W | Matches any character that is not letters, numbers, underscores, or Chinese characters |
| \S | Matches any character that is not whitespace |
| \D | Matches any non-digit character |
| \B | Match is not at the beginning or end of the word |
| [^x] | Matches any character except x |
| [^aeiou] | Matches any character except aeiou. |
| character | describe |
|---|---|
| ^\d+$ | //Match non-negative integers (positive integers + 0) |
| //Match integers^\d+(\.\d+)?$ | //Match non-negative floating point numbers (positive floating point numbers + 0) |
| ^(([0-9]+\.[0-9]*[1-9][0-9]*)|([0-9]*[1-9][0-9]*\.[0-9]+)|([0-9]*[1-9][0-9]*))$ | //Match positive floating point numbers |
| ^((-\d+(\.\d+)?)|(0+(\.0+)?))$ | //Match non-positive floating point numbers (negative floating point numbers + 0) |
| ^(-(([0-9]+\.[0-9]*[1-9][0-9]*)|([0-9]*[1-9][0-9]*\.[0-9]+)|([0-9]*[1-9][0-9]*)))$ | //Match negative floating point numbers |
| ^(-?\d+)(\.\d+)?$ | //Match floating point numbers |
| ^[A-Za-z]+$????????? | //Match a string consisting of 26 English letters |
| ^[A-Z]+$ ??? | //Match a string consisting of 26 uppercase English letters |
| ^[a-z]+$ | //Match a string consisting of 26 lowercase English letters |
| ^[A-Za-z0-9]+$ | //Match a string consisting of numbers and 26 English letters |
| ^\w+$ | //Match a string consisting of numbers, 26 English letters, or underscores |
| ^[\w-]+(\.[\w-]+)*@[\w-]+(\.[\w-]+)+$ | //Match email address |
| ^[a-zA-z]+:// match(\w+(-\w+)*)(\.(\w+(-\w+)*))*(\?\S*)?$ | //match url |
| [\u4e00-\u9fa5] | Regular expression to match Chinese characters |
| [^\x00-\xff] | Match double-byte characters (including Chinese characters) |
| \n[\s| ]*\r | Regular expression to match empty lines |
| /<(.*)>.*<\/>|<(.*)\/>/ | Regular expression to match HTML tags |
| (^\s*)|(\s*$) | Regular expression matching leading and trailing spaces |
| \w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)* | Regular expression to match email addresses |
| ^[a-zA-z]+://(\w+(-\w+)*)(\.(\w+(-\w+)*))*(\?\S*)?$ | Regular expression to match URL |
| ^[a-zA-Z][a-zA-Z0-9_]{4,15}$ | Whether the matching account is legal (starting with a letter, 5-16 bytes allowed, alphanumeric underscores allowed) |
| (\d{3}-|\d{4}-)?(\d{8}|\d{7})? | Match domestic phone numbers |
| ^[1-9]*[1-9][0-9]*$ | Match Tencent QQ number |