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(PHP 4, PHP 5)
link — Erzeugt einen harten Link
link() erzeugt einen harten Link
Der Linkname.
Ziel des Links.
Gibt bei Erfolg TRUE zurück. Im Fehlerfall wird FALSE zurückgegeben.
Hinweis: Nur für Windows: Diese Funktion setzt voraus, dass PHP in einem erhöhten Modus oder mit deaktivierter Benutzerkontensteuerung (UAC) läuft.
| Version | Beschreibung |
|---|---|
| 5.3.0 | Diese Funktion ist nun verfügbar unter Windows-Plattformen (Vista, Server 2008 or neuer). |
Beispiel #1 Erstellen eines harten Links
<?php
$from_path = 'quelle.ext'; // Die ist die bereits existierende Datei
$to_path = 'neuedatei.ext'; // Dies ist der Dateiname, auf den verlinkt
// werden soll
link($from_path, $to_path);
?>
Hinweis: Diese Funktion kann nicht mit entfernten Dateien arbeiten, da der Zugriff auf die Datei, die bearbeitet werden soll, über das Dateisystem des Servers möglich sein muss.
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.
>> Be aware that the filesystem of the target and the link must be the same,
>> otherwise the link will fail! (Linking files over different filesystems doesn't work under Unix).
Using debian sid, 2.6.24-17-generic, that is definitely not true.
As others have noted, the parameter order can seem a little awkward. Here's a mnemonic for remembering the order:
In UNIX, commands go like this:
> command input output
The link command is no different:
> ln infile outfile
...and PHP respects that convention.
Due to the acquisition of Winternals by Microsoft, the previous link to junction.exe doesn't work anymore. The file has been moved to http://www.microsoft.com/technet/
sysinternals/FileAndDisk/Junction.mspx
(without the newline)
For those that find the order of the arguments unclear, here is a more verbose description:
<?php
$source = "something.ext"; // This is the file that already exists
$dest = "newfile.ext"; // This the filename that you want to link it to
link($source, $dest);
?>
Make link recursively :
<?php
function makeRecusLink($orig, $dest)
{
if (is_dir($orig)) {
if (substr($orig, -1) != '/') {
$orig .= '/';
}
$handle = opendir($orig);
while (false !== ($file = readdir($handle))) {
if ($file != '.' && $file != '..') {
$path = $orig.$file;
if (is_file($path)) {
@link($path, $dest.'/'.$file);
} else if (is_dir($path)) {
@mkdir($dest.'/'.$file, 0755);
makeRecusLink($path, $dest.'/'.$file);
}
}
}
}
closedir($handle);
}
?>
Be aware that the filesystem of the target and the link must be the same, otherwise the link will fail! (Linking files over different filesystems doesn't work under Unix).
For a backup utility I needed link-like functionality on a windows system. As it isn't availible on windows, i tried to do it myself with the help of some tools. All you need is junction.exe from sysinternals in your %PATH%.
<?php
if(!function_exists('link')){ // Assume a windows system
function link($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
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
I think kop is confused regarding the semantics of link's argument order. The user's comment states that target should not already exist, suggesting that it is the target that is being created. As with the UNIX hardlink, ln(1), the target is the existing file. I think kop meant to say php's link() will return an error if the second parameter, the link being created, already exists.
Also, as with the UNIX system call link will fail if the link being created exists on a different filesystem.
Note that link() will not work if the target already exists, at least as of php 4.1.2.
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