Regular expression match backslash--match a backslash to use four backslash

Match a backslash in a regular expression to use four backslashes, 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 2 points to make clear:

1. The string inside means that the slash requires two slashes such as "\ \"

2. The slash in the regular expression needs to be turned, and is marked with "\ \".

This is a better explanation:

We will first represent the slash "\ \" Inside the regular expression, and then use the string representation. And these 2 slashes need an escape character, which makes 4 slashes in the regular expression to represent a slash.

Regular expression match backslash--match a backslash to use four backslash