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In PHP, the operation of files and directories is very powerful, where the link() function is a built-in function for creating hard links. Although it is not commonly used like file read or write functions, it can provide a very efficient solution in certain scenarios. This article will analyze the basic usage of the link() function in detail and combine it with actual application scenarios to help you better understand its value.
The function of the link() function is to create a new hard link for an existing file. In other words, two file names with different paths will point to the same physical file content. This linking method is different from soft links, and hard links are more like "another entry" to file content.
The function definition is as follows:
bool link(string $target, string $link)
$target : The target file to be linked (already exists).
$link : The path of the newly created link file.
Return true if the link is created successfully, otherwise return false .
Here is a simple example showing how to create a hard link using link() :
<?php
$target = '/var/www/html/original.txt';
$link = '/var/www/html/copy.txt';
if (link($target, $link)) {
echo "Hard link creation successfully。";
} else {
echo "Hard link creation failed。";
}
?>
After successful execution, original.txt and copy.txt point to the same physical file content, and changes to any of the file contents will be reflected on the other.
Hard links created with link() have the following characteristics:
Share inode : Hard-linked files share the same inode as the original file.
Synchronous update : The content changes of any file will be reflected in another file.
Deletion has no effect : Deleting one of the link files does not affect the actual file content unless all hard links are deleted.
Applicable to files only : You cannot create hard links for directories (unless you use system-level privileges).
Local file systems only : Hard links cannot cross file systems.
While hard links are not common in daily development, they are very useful in the following scenarios:
For example, a website needs to reference the same configuration file in multiple modules, and you don't want to copy one copy every time. Using link() can make the same "file" appear in multiple module paths, reducing redundancy.
link('/var/www/html/config/global.conf', '/var/www/html/moduleA/config.conf');
Some backup strategies save daily snapshots through hard links, only actually create new files when the content changes, and other unchanged parts share content through hard links, thus greatly reducing waste of storage space.
For example:
link('/var/www/html/data/log.txt', '/backup/2025-05-26/log.txt');
Without using the version control system, a "status file" can be saved at a specific point in time through a hard link. Even if the original file is modified, the old version can still be accessed through the hard link path.
The following points should be paid attention to when using link() :
PHP scripts must have permission to create link files.
In the Windows environment, there is limited support for hard links, and NTFS is required and the corresponding permissions are enabled.
The two paths to create a hard link must be in the same file system.
Although the link() function of PHP is not used frequently, it provides an efficient and underlying file operation method, which is especially suitable for advanced application scenarios such as backup, version control or resource sharing. Mastering this function will help you understand more deeply how the file system and PHP are combined.
Through hard link technology, we can implement smarter file management strategies, especially in systems with limited resources or high performance requirements, link() may be the "unpopular weapon" you need.
For more relevant practical tutorials, you can visit:
echo file_get_contents('https://gitbox.net/php/link-tutorial');
