Reference-PHP Manual notes

The reference in PHP means that the contents of the same variable are accessed with different variable names, similar to the UNIX file name and the file itself (the variable name is the directory entry, the variable content is the file itself, that is, accessing the same file with different directory entries), which can be seen as a hard link in the UNIX filesystem.

There are two types of links in the file system, one called hard link, and the other is called Symbolic link (symbolic). By default, the LN command produces a hard link. A hard join refers to a connection made through an index node. In a Linux file system, files saved in a disk partition are assigned a number, called the index node number (INODEINDEX), regardless of the type. In Linux, multiple file names point to the same index node that exists. In general, this connection is a hard connection. The purpose of a hard connection is to allow a file to have multiple valid pathname, so that users can establish a hard connection to important files to prevent "accidental deletion" of the function. The reason for this is as above, because there is more than one connection to the index node that should be the directory. Deleting only one connection does not affect the index node itself and other connections, and the connection to the file's data block and directory will be released only if the last connection is deleted. In other words, the file is actually deleted. In contrast to a hard connection, there is another connection in the Lnux system, called a symbolic connection (SYMBILC link), also known as a soft connection. A soft link file is a bit like a shortcut to Windows. It is actually a kind of special file. In a symbolic connection, a file is actually a text file that contains location information for another file.

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Reference-PHP Manual notes