Why doesn't the regular expression in my Go program match?

As the Go language becomes more and more widely used in various industries, regular expressions are used more and more often. However, sometimes we encounter a problem: our regular expression is written correctly in the code, but it cannot match the text we want. At this time, what should we do?

First, we need to understand some basic knowledge of regular expressions. Regular expressions are a powerful text matching tool that can quickly match parts of text that match certain rules. But this kind of rule must be written very accurately, otherwise it will cause matching failure. Here, we need to pay attention to two aspects:

1. How to write regular expressions
2. Types of data in the program

Let’s introduce them separately:

1. How to write regular expressions

Regular expressions are a very powerful tool for string operations and are also an important part of many program applications. Regular expressions in the Go language are implemented based on the RE2 library, and are slightly different in some details. When using regular expressions, we need to pay attention to the following points:

1. Correct regular expressions
Regular expressions must comply with grammatical specifications. If a regular expression has incorrect syntax, the program will not compile. Therefore, when writing regular expressions, we need to carefully check each character to ensure the correctness of the regular expression.

2. Matching mode
In the RE2 library, the Go language provides the following three matching modes:

i.默认模式 - "(?i)"，表示忽略大小写。
ii.多行模式 - "(?m)"，表示按行匹配。
iii.单行模式 - "(?s)"，表示"."可以匹配任何字符，包括换行符。

3. Repeatability of regular expressions
In regular expressions Repeatability refers to the repetition of a certain character multiple times. What needs to be noted here is that when using metacharacters such as "*", " ", "?", "{}", etc., you need to carefully consider their usage positions, otherwise the matching will fail.

2. Type of data in the program

In the program, the data type will also affect the matching result of the regular expression. Because regular expression matching is based on strings as operation objects, if we do not handle the data type correctly, it may cause the regular expression to fail to match. The following are some examples of errors:

1. Directly pass non-string data types into regular expressions

For example, if you pass an integer type data into a regular expression, it will Causes the Go language to throw a type mismatch error because the regular expression expects to receive a parameter of type string.

2. Escape characters are used in strings

In regular expressions, some characters need to use escape characters to represent themselves. However, in the Go language, strings also use escape characters to represent special characters, such as double quotes, newlines, etc. This may lead to misinterpretation of regular expressions. For example:

regexp.MatchString("\d", "3") //The match is successful
regexp.MatchString("d", "3") //An error will occur during compilation

When using regular expressions, we need to pay special attention to the escape characters in the string to ensure accurate matching of the regular expression.

Finally, we need to add some commonly used regular expressions:

1. Match email addresses:

^[a-zA-Z0-9_-] @[a -zA-Z0-9_-] (.[a-zA-Z0-9_-] ) $

2. Match URL address:

^((https?|ftp|file) ://)?([da-z.-] ).([a-z.]{2,6})([/w .-])/?$

3 .Match mobile phone number:

^1[3456789]d{9}$

Through the explanation of this article, we hope that readers can have a clearer understanding of the correct way of writing regular expressions and the data in the program The correct calling method of the type, so as to better use the Go language for regular expression matching.

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