What is the use of regular expression boundary characters?

The functions of regular expression boundary characters are: 1. Determine the starting position of the match and ensure matching from the beginning of the string; 2. Determine the end position of the match and specify the end position of the match; 3. Exclude specific characters to ensure that only independent words are matched; 4. Precisely control the matching range; 5. Exclude the influence of escaped characters to ensure that the literal meaning is matched rather than the escaped result; 6. Distinguish word boundaries and make it clear Word boundaries to avoid this confusion; 7. Match fixed-length strings, which can accurately match fixed-length strings.

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

Boundary characters in regular expressions are used to define the start and end positions of the matching pattern. They can be used to precisely control the matching range to ensure that only strings that meet the requirements are matched. Boundary characters have the following effects:

1. Determine the starting position of the match: Use the boundary character to specify the starting position of the match, ensuring that the match starts from the beginning of the string. For example, using ^ as the delimiter, the regular expression will only match the beginning of the string.

2. Determine the end position of the match: Similar to the starting position, the boundary character can also specify the end position of the match. For example, using $ as the delimiter, the regular expression will only match the end of the string.

3. Exclude specific characters: Some boundary characters can exclude specific characters or patterns. For example, use \b to match word boundaries, excluding letters or numbers within words. This ensures that only standalone words are matched, rather than substrings contained within other words.

4. Precisely control the matching range: By combining the start and end boundary characters, you can precisely control the matching range. For example, ^abc$ will only match the string "abc" and no other characters.

5. Exclude the impact of escape characters: In regular expressions, some characters have special escape meanings. For example, \n represents a newline character. Using delimiters ensures that the literal meaning is matched rather than the escaped result.

6. Distinguish between word boundaries: In some cases, you may want to match the complete content of a word, rather than partially matching parts of other words. Use boundary markers to clarify word boundaries and avoid this confusion.

7. Match fixed-length strings: Use a combination of boundary characters and numbers of a specific length to accurately match fixed-length strings. For example, ^.{5}$ will match a string of length 5.

In short, the boundary characters of regular expressions play an important role in determining the matching range, accurately controlling string matching, and excluding specific characters. They help you write regular expressions more accurately and achieve finer control when working with text data.

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