link()

(PHP 4, PHP 5, PHP 7)

建立一个硬连接

说明

link(string $target,string $link): bool

link()建立一个硬连接。

参数

$target

要链接的目标。

$link

链接的名称。

返回值

成功时返回TRUE，或者在失败时返回FALSE。

注释

Note:Windows下：该功能需要以 elevated 模式运行，或者关闭 UAC。

更新日志

范例

Creating a simple hard link

<?php
$target = 'source.ext'; // This is the file that already exists
$link = 'newfile.ext'; // This the filename that you want to link it to
link($target, $link);
?>

注释

Note:此函数不能作用于远程文件，被检查的文件必须是可通过服务器的文件系统访问的。

参见

• symlink() 建立符号连接
• readlink() 返回符号连接指向的目标
• linkinfo() 获取一个连接的信息

to clarify:
in unix/linux:
hardlinks (by this function) cannot go across different filesystems.
softlinks can point anywhere.
in linux, hardlinking to directory is not permited.

For a backup utility I needed link-like functionality on a windows system. As it isn't availible on windows, i tried to do it myself with the help of some tools. All you need is junction.exe from sysinternals in your %PATH%.
<?php
if(!function_exists('link')){ // Assume a windows system
  function link($target, $link){
    if(is_dir($target)){
      // junctions link to directories in windows
      exec("junction $link $target", $lines, $val);
      return 0 == $val;
    }elseif(is_file($target)){
      // Hardlinks link to files in windows
      exec("fsutil hardlink create $link $target", $lines, $val);
      return 0 == $val;
    }
    
    return false;
  }
}
?>
http://www.sysinternals.com/Utilities/Junction.html

In at least php-5.3 (linux-2.6.38.6) a process owned by apache could make a link() in a directory owned by apache, to a file owned by webmaster to which it had group read permissions. In php-7.0 (linux-4.13.16) that results in a "permission denied". Either the target file must be owned by apache or one must use copy() instead (so that ownership changes to apache).

I noticed that, differently from Unix ln command, the second parameter can´t be a directory name, i.e., if you want to create a link with the same filename of the target file (obviously on different directories), you must specify the filename on the link parameter.
Example:
Unix ln command:
ln /dir1/file /dir2/  // ok, creates /dir2/file link
PHP link function:
link ("/dir1/file", "/dir2/");  // wrong, gives a "File exists" warning
link ("/dir1/file", "/dir2/file");  // ok, creates /dir2/file link