Regular Expression matching backslash

The regular expression matches a backslash with four backslash. Why?

Analyze "\\\\". The first slash is the escape character, the second slash is the slash itself, the third slash is the escape character, and the fourth slash is the slash itself.

There are two points to be clear:

1. In the string, two slashes are required, for example, "\".

2. The slash in the regular expression needs to be converted. It is marked.

This is a better explanation:

We first need to represent the slash "\" in the regular expression, and then represent it with a string. The two slashes need an escape character respectively, so that the four slashes represent a slash in the regular expression.