is_link()

(PHP 4, PHP 5, PHP 7)

判断给定文件名是否为一个符号连接

说明

is_link(string $filename): bool

判断给定文件名是否为一个符号连接。

参数

$filename: 文件的路径。

返回值

如果文件存在并且是一个符号连接则返回TRUE，否则返回FALSE。

范例

创建并确认一个文件是否为符号连接

<?php
$link = 'uploads';
if (is_link($link)) {
    echo(readlink($link));
} else {
    symlink('uploads.php', $link);
}
?>

错误／异常

失败时抛出E_WARNING警告。

注释

Note:此函数的结果会被缓存。参见clearstatcache()以获得更多细节。

Tip

自 PHP 5.0.0 起,此函数也用于某些URL 包装器。请参见支持的协议和封装协议以获得支持stat()系列函数功能的包装器列表。

参见

is_dir() 判断给定文件名是否是一个目录
is_file() 判断给定文件名是否为一个正常的文件
readlink() 返回符号连接指向的目标

To find out whether a file is hardlinked to another filename, check the number of links of the stat() output. If it is >1 there is another filename for that file.
To find out whether two filenames are pointing to the same file, check the inode number of those 2 filenames. If it is equal, the 2 filenames are hardlinked together.

A workaround for Windows LNK files:
<?php
function _is_link($filename)
{
  if(is_link($filename))
    return true;
  $ext = substr(strrchr($filename, '.'), 1);
  if(strtolower($ext) == 'lnk')
  {
    return (_readlink($filename) ? true : false);
  }
  return false;
}
function _readlink($file)
{
  if(file_exists($file))
  {
    if(is_link($file))
    {
      return readlink($file);
    }
    // Get file content
    $handle = fopen($file, "rb");
    $buffer = array();
    while(!feof($handle))
    {
      $buffer[] = fread($handle, 1);
    }
    fclose($handle);
    // Test magic value and GUID
    if(count($buffer) < 20)
      return false;
    if($buffer[0] != 'L')
      return false;
    if((ord($buffer[4]) != 0x01) ||
      (ord($buffer[5]) != 0x14) ||
      (ord($buffer[6]) != 0x02) ||
      (ord($buffer[7]) != 0x00) ||
      (ord($buffer[8]) != 0x00) ||
      (ord($buffer[9]) != 0x00) ||
      (ord($buffer[10]) != 0x00) ||
      (ord($buffer[11]) != 0x00) ||
      (ord($buffer[12]) != 0xC0) ||
      (ord($buffer[13]) != 0x00) ||
      (ord($buffer[14]) != 0x00) ||
      (ord($buffer[15]) != 0x00) ||
      (ord($buffer[16]) != 0x00) ||
      (ord($buffer[17]) != 0x00) ||
      (ord($buffer[18]) != 0x00) ||
      (ord($buffer[19]) != 0x46))
    {
      return false;
    }
    $i = 20;
    if(count($buffer) < ($i + 4))
      return false;
    $flags = ord($buffer[$i]);
    $flags = $flags | (ord($buffer[++$i]) << 8);
    $flags = $flags | (ord($buffer[++$i]) << 16);
    $flags = $flags | (ord($buffer[++$i]) << 24);
    $hasShellItemIdList = ($flags & 0x00000001) ? true : false;
    $pointsToFileOrDir = ($flags & 0x00000002) ? true : false;
    if(!$pointsToFileOrDir)
      return false;
    if($hasShellItemIdList)
    {
      $i = 76;
      if(count($buffer) < ($i + 2))
        return false;
      $a = ord($buffer[$i]);
      $a = $a | (ord($buffer[++$i]) << 8);
      
    }
    $i = 78 + 4 + $a;
    if(count($buffer) < ($i + 4))
      return false;
    $b = ord($buffer[$i]);
    $b = $b | (ord($buffer[++$i]) << 8);
    $b = $b | (ord($buffer[++$i]) << 16);
    $b = $b | (ord($buffer[++$i]) << 24);
    $i = 78 + $a + $b;
    if(count($buffer) < ($i + 4))
      return false;
    $c = ord($buffer[$i]);
    $c = $c | (ord($buffer[++$i]) << 8);
    $c = $c | (ord($buffer[++$i]) << 16);
    $c = $c | (ord($buffer[++$i]) << 24);
    $i = 78 + $a + $b + $c;
    if(count($buffer) < ($i +1))
      return false;
    $linkedTarget = "";
    for(;$i < count($buffer); ++$i)
    {
      if(!ord($buffer[$i]))
        break;
      $linkedTarget .= $buffer[$i];
    }
    if(empty($linkedTarget))
      return false;
    
    return $linkedTarget;
  }
  return false;
}
if(_is_link('test.lnk'))
{
  echo _readlink('test.lnk');
}
?>

For me (Debian Sarge VPS) is_link returns true even for directories if you don't add a trailing slash to the filename.
<?php
if ($dir{strlen($dir)-1} == '/') $dir = substr($dir, 0, -1);
is_link($dir);
?>
This works for me. It can't detect a symlink somewhere in a complete path, though (i.e. is_link(/www/somedir/file.php) will return false, just as is_link(/www/) would)

Careful when using is_link() in thread-safe builds with the self-referential directory entry ".". On ZTS builds is_link("/home/symlink/.") will return true whereas it returns false on non-ZTS builds.

On windows, take care that is_link returns false for Junctions.
Ways of telling apart a directory from a junction include doing both a stat() and and lstat() call and checking if there is any difference in the results

@radon8472 at hotmail dot com
The windows .lnk-things are real files, the explorer only treats them like links. Try to open one with Win+R->"notepad X:\Path\Visiblefilename.lnk You will see much 0-Bytes, but the linked path is displayed right on the screen. It should be possible to do the same by php.

On my SuSE 7.2 is_link does not work on directories, but to find out, if a dir is a link, I use now this:
$linkdir = $path.$linkdirname;
if (realpath($linkdir) != realpath($path)."/".$linkdirname):
//$linkdir is a symbolic linked dir!
...
and this works fine :-)
Andreas Dick

This function returns "false" for windows *.lnk files (tested under windows XP). 
filetype also returns "file" an not "link" like expected.
I didn`t find a solution for this.

On Mac OSX, to see if a file is a FInder alias:
<?PHP
if( getFinderAlias( $someFile , $target ) ) {
 echo $target;
}
else {
 echo "File is not an alias";
}
function getFinderAlias( $filename , &$target ) {
$getAliasTarget = <<< HEREDOC
  -- BEGIN APPLESCRIPT --
  set checkFileStr to "{$filename}"
  set checkFile to checkFileStr as POSIX file
  try
    tell application "Finder"
      if original item of file checkFile exists then
        set targetFile to (original item of file checkFile) as alias
        set posTargetFile to POSIX path of targetFile as text
        get posTargetFile
      end if
    end tell
  end try
  -- END APPLESCRIPT --
HEREDOC;
$runText = "osascript << EOS\n{$getAliasTarget}\nEOS\n";
$target = trim( shell_exec( $runText ) );
return ( $target == "" ? false : true );
}
?>