What is the basic syntax of regular expressions?
Regular expressions are tools used to match string patterns, consisting of ordinary characters (such as letters, numbers, and symbols) and special characters (known as metacharacters). The basic syntax of regular expressions includes the following parts:
- Regular characters: Regular characters refer to letters, numbers, and some special characters that are directly represented in regular expressions.
- Metacharacters are special characters that have specific meanings and are used to specify matching rules. Common metacharacters include:
- ^: indicates the beginning of a string.
- $: Indicates the end of a string.
- . represents a match for any character
- *: indicates matching the preceding character zero or more times
- +: Indicates matching the preceding character one or more times.
- ?: indicates matching the preceding character zero or one time.
- []: Represents matching any single character within it.
- Parentheses are used to indicate grouping.
- Quantifiers: Quantifiers are used to specify the number of times a match should occur. Commonly used quantifiers include:
- {n}: indicates matching the preceding character exactly n times.
- {n,} : indicates matching the preceding character at least n times.
- {n,m}：indicates matching the previous character at least n times and at most m times
- Escape character: Some characters have special meanings in regular expressions, and if you want to match them literally, you need to use the escape character \ to escape them.
- Modifiers: Modifiers are used to specify some characteristics of the matching pattern, such as case sensitivity, multiline matching, etc. Commonly used modifiers include:
- i: case-insensitive
- “g: indicates a global match”
- m: indicates matching across multiple lines
In general, the basic syntax of regular expressions consists of ordinary characters, metacharacters, quantifiers, escape characters, and modifiers. By combining these elements, a variety of complex matching rules can be constructed.
