What does regular expression () mean?

Regular expression () is the meaning of extracting matching strings. It mainly has two functions: 1. Grouping. In regular expressions, parentheses can be used to combine some characters to form a group, which is usually used to determine priority, number of repetitions or special matching rules; 2. Capture, When specific text is matched within the brackets in the regular expression, the text can be saved for subsequent use, for replacement operations or reference in other regular expressions, etc.

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

The brackets () in regular expressions have two main functions: grouping and capturing.

1. Grouping: In regular expressions, parentheses can be used to group some characters together to form a group. This is typically used to determine priority, repetitions, or special matching rules. For example, (ab) matches the characters a and b together as a whole.

2. Capture: When specific text is matched within the brackets in the regular expression, the text can be saved for subsequent use. The captured content can be used in replacement operations or referenced in other regular expressions. For example, in a replacement operation, you can use \1 to refer to the first captured content.

Here are some examples to illustrate the use of brackets in regular expressions:

1. Grouping: In regular expressions, brackets can be used Combine multiple characters into a whole. For example, the regular expression (abc) will match "abc" as a whole, not the individual characters a, b, or c.

2. Capture: When the content within brackets matches the target text, the content can be saved for subsequent use. For example, in a replacement operation, you can use \1 to refer to the first captured content. Suppose we have a string "Hello, 123" and we want to replace the number part with "[number]". We can use regular expressions (\d) to match and replace. In this way, "Hello, 123" will be replaced by "Hello, [number]".

In short, parentheses in regular expressions have two main functions: grouping and capturing. By using parentheses, we can specify matching patterns more precisely and save the matched content for later use.

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