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What exactly is a regular expression?
When writing programs or web pages that process strings, there is often a need to find strings that match some complex rules. Regular expressions are tools used to describe these rules. In other words, regular expressions are codes that record text rules.
Common metacharacters
| Code/Syntax | Description |
|---|---|
| . | Matches any character except newline |
| \w | Match letters or numbers or underscores |
| \s | Matches any whitespace character |
| \d | Match numbers |
| \b | Match the beginning or end of a word |
| ^ | Match the beginning of a string |
| $ | Match the end of the string |
Common qualifiers
| Code/Syntax | Description |
|---|---|
| * | Repeat zero or more times |
| + | Repeat one or more times |
| ? | Repeat zero or one time |
| {n} | Repeat n times |
| {n,} | Repeat n times or more |
| {n,m} | Repeat n to m times |
Commonly used antonyms
| Code/Syntax | Description |
|---|---|
| \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-numeric character |
| \B | matches a position that is not the beginning or end of a word |
| [^X] | Matches any character except x |
| [^aeiou] | Matches any character except the letters aeiou |