Video tutorial for learning PHP: The importance of file naming rules

The file name is to make it easier for people to distinguish different files in the computer, and to set a designated name for each file. It consists of the main name of the file and its extension.

The DOS operating system stipulates that the file name consists of the file main name and the extension name. The file main name consists of 1 to 8 characters. Illegal characters in the Linux file name . The extension name consists of 1 to 3 characters. The name and extension are separated by a small dot, often called the 8.3 rule. (Recommended learning: PHP video tutorial)

The format is as follows:

□□□□□□□□.□□□

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For example: G9401.DBF, here G9401 is the main name of the linux scheduled task, and DBF is the extension name. The characters that can be used for the file main name and extension are: 
 (1) English letters: A—z (upper and lower case equivalent) 
 (2) Number: 0-9
 (3) Chinese characters
 (4) Special symbols: $#&@ ()-[]^~, etc. 
 (5) Various control characters and the following characters cannot be used in file names: 
/|:"*?
Because those characters have been used for other purposes. 
windows breaks through the restrictions of DOS on file naming rules and allows the use of long file namesIllegal characters in Linux file names. The main naming rules are as follows:
 (1) The maximum length of the file name can be 255 characters. 
 (2) You can use an extension name. The extension name is used to indicate the file type. You can also use an extension name with multiple separators. For example, win.ini.txt is a legal file name, but its file type is determined by the last extension. 
 (3) Spaces are allowed in file names, but the following characters are not allowed (Chinese input method status): /|:"*?
 (4) The windows system displays different cases of letters in file names, but does not distinguish between upper and lower case when using them. 
The file name is an indication of the existence of the file, and the operating system controls and manages it according to the file name. Different operating systems have slightly different rules for file naming, that is, the format and thickness of the file name vary from system to system. Such as :UNIX/LINUX systems distinguish the case of file names, while some systems do not distinguish, such as: MS-DOS and WINDOWS.
The file extension is used to distinguish the attributes of the file. In some systems, it is not perceived by the system. For example: in UNIX/LINUX systems, there is no difference between the hello.c file and the helloc file for the system. Adding the extension .c is the same as not adding it. The system does not know what file it is. But after the user adds .c, it is easier for the user to understand that it is a C language source code file.
 However, in MS-DOS and WINDOWS systems, file extensions are system-aware. In WINDOWS, different file extensions have their associated programs to open. This extension is not only such as txt, etc. Except for the original ones, the rest are usually registered in the system when installing the software. You can see its related information under the HKEY-CLASSES-ROOT root key in the registry.
If you change the file extension to one that is not recognized by the system, you will be prompted to select the program to open it when opening it. For example, if you change hello.txt to hello.123, you can also see that the icon has also changed, becoming Unknown. And for WORD files such as .doc format, because it was developed by MICROSOFT, it maintains good compatibility. When sensing, the system not only detects the extension name, but also detects the internal format mark of the file, so although .doc is Change it to other characters. In a system with WORD installed, the system can still associate it with WORD for opening.
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