tempnam

(PHP 4, PHP 5, PHP 7, PHP 8)

tempnam — Create file with unique file name

Description

tempnam(string $directory, string $prefix): string|false

Creates a file with a unique filename, with access permission set to 0600, in the specified directory. If the directory does not exist or is not writable, tempnam() may generate a file in the system's temporary directory, and return the full path to that file, including its name.

Parameters

directory: The directory where the temporary filename will be created.
prefix: The prefix of the generated temporary filename.

Note: Only the first 63 characters of the prefix are used, the rest are ignored. Windows uses only the first three characters of the prefix.

Return Values

Returns the new temporary filename (with path), or false on failure.

Changelog

Version	Description
7.1.0	tempnam() now emits a notice when falling back to the temp directory of the system.

Examples

Example #1 tempnam() example

<?php
$tmpfname = tempnam("/tmp", "FOO");

$handle = fopen($tmpfname, "w");
fwrite($handle, "writing to tempfile");
fclose($handle);

// do something here

unlink($tmpfname);
?>

Notes

Note: If PHP cannot create a file in the specified directory parameter, it falls back on the system default. On NTFS this also happens if the specified directory contains more than 65534 files.

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User Contributed Notes 22 notes

down

koyama ¶

15 years ago

Watch out using a blank $dir as a "trick" to create temporary files in the system temporary directory.



<?php

$tmpfname = tempnam('', 'FOO'); // not good

?>



If an open_basedir restriction is in effect, the trick will not work. You will get a warning message like



Warning: tempnam() [function.tempnam]: open_basedir restriction in effect.

File() is not within the allowed path(s): (/var/www/vhosts/example.com/httpdocs:/tmp)



What works is this:



<?php

$tmpfname = tempnam(sys_get_temp_dir(), 'FOO'); // good

?>

down

Sebastian Kun ¶

19 years ago

If you go to the linux man page for the C function tempnam(3), you will see at the end "Never use this function. Use mkstemp(3) instead." But php's tempnam() function doesn't actually use tmpnam(3), so there's no problem (under Linux, it will use mkstemp(3) if it's available).

down

php at REMOVEMEkennel17 dot co dot uk ¶

19 years ago

Note that tempnam returns the full path to the temporary file, not just the filename.

down

stanislav dot eckert at vizson dot de ¶

7 years ago

Please note that this function might throw a notice in PHP 7.1.0 and above. This was a bugfix: https://bugs.php.net/bug.php?id=69489

You can place an address operator (@) to sillence the notice:

<?php

if ($tmp = @tempnam() !== false) {
  // ...
}

?>

Or you could try to set the "upload_tmp_dir" setting in your php.ini to the temporary folder path of your system. Not sure, if the last one prevents the notices.

down

Jason Pell ¶

17 years ago

I want to guarantee that the file will be created in the specified directory or else the function should return FALSE, I have a simple function that works, but I am unsure if its a potential security issue.

function dir_tempnam($dir, $prefix)
{
    $real_dir_path = realpath($dir);
    if (substr($real_dir_path, -1) != '/')
        $real_dir_path .= '/';
    
    $tempfile = tempnam($real_dir_path, $prefix);
    $name = basename($tempfile);
    
    if(is_file($real_dir_path.$name))
        return $name;
    else
    {
        @unlink($name);
        return FALSE;
    }
}

This function returns just the name of the temporary file in the specified directory, or FALSE.

Obviously it could return the entire $tempfile, but in my case, I actually want the basename value seperate.

down

Artur Graniszewski ¶

14 years ago

tempnam() function does not support custom stream wrappers registered by stream_register_wrapper(). 

For example if you'll try to use tempnam() on Windows platform, PHP will try to generate unique filename in %TMP% folder (usually: C:\WINDOWS\Temp) without any warning or notice.

<?php

// << ...custom stream wrapper goes somewhere here...>>

echo '<pre>';
error_reporting(E_ALL);
ini_set('display_errors', true);
clearstatcache();
stream_register_wrapper('test', 'MemoryStream');

mkdir('test://aaa');
mkdir('test://aaa/cc');
mkdir('test://aaa/dd'); 
echo 'PHP '.PHP_VERSION;
echo '<br />node exists: '.file_exists('test://aaa/cc');
echo '<br />node is writable: '.is_writable('test://aaa/cc');
echo '<br />node is dir: '.is_dir('test://aaa/cc');
echo '<br />tempnam in dir: '.tempnam('test://aaa/cc', 'tmp');
echo "<br /></pre>";

?>

ouputs:
--------------------
PHP 5.2.13
node exists: 1
node is writable: 1
node is dir: 1
tempnam in dir: C:\Windows\Temp\tmp1D03.tmp

If you want to create temporary file, you have to create your own function (which will probably use opendir() and fopen($filename, "x") functions)

down

anakin dot skyw at gmx dot de ¶

20 years ago

>Under UNIX (where you can rename onto an extant file and so I used link), you will have to remove both the link and the link's target.

Couldn't you do
<?php
       if ($newFileCreated) {
           unlink ($sysFileName);
           return $newFileName;
       }
?>
and get the same semantics as the windows version?

down

Ron Korving ¶

18 years ago

This function creates a temporary directory. The previous example given could bug if between the unlink() and mkdir() some process creates the same directory or file. This implementation is faster too.

<?php
  function tempdir($dir, $prefix='', $mode=0700)
  {
    if (substr($dir, -1) != '/') $dir .= '/';

    do
    {
      $path = $dir.$prefix.mt_rand(0, 9999999);
    } while (!mkdir($path, $mode));

    return $path;
  }
?>

down

bishop ¶

20 years ago

Creating a temporary file with a specific extension is a common requirement on dynamic websites. Largely this need arises from Microsoft browsers that identify a downloaded file's mimetype based on the file's extension.

No single PHP function creates a temporary filename with a specific extension, and, as has been shown, there are race conditions involved unless you use the PHP atomic primitives.

I use only primitives below and exploit OS dependent behaviour to securely create a file with a specific postfix, prefix, and directory.  Enjoy.

<?php
function secure_tmpname($postfix = '.tmp', $prefix = 'tmp', $dir = null) {
    // validate arguments
    if (! (isset($postfix) && is_string($postfix))) {
        return false;
    }
    if (! (isset($prefix) && is_string($prefix))) {
        return false;
    }
    if (! isset($dir)) {
        $dir = getcwd();
    }

    // find a temporary name
    $tries = 1;
    do {
        // get a known, unique temporary file name
        $sysFileName = tempnam($dir, $prefix);
        if ($sysFileName === false) {
            return false;
        }

        // tack on the extension
        $newFileName = $sysFileName . $postfix;
        if ($sysFileName == $newFileName) {
            return $sysFileName;
        }

        // move or point the created temporary file to the new filename
        // NOTE: these fail if the new file name exist
        $newFileCreated = (isWindows() ? @rename($sysFileName, $newFileName) : @link($sysFileName, $newFileName));
        if ($newFileCreated) {
            return $newFileName;
        }

        unlink ($sysFileName);
        $tries++;
    } while ($tries <= 5);

    return false;
}
?>

The isWindows function is mostly left as an exercise for the reader. A starting point is below:

<?php
function isWindows() {
    return (DIRECTORY_SEPARATOR == '\\' ? true : false);
}
?>

Like tempnam(), this function requires you to cleanup your own files later. Under UNIX (where you can rename onto an extant file and so I used link), you will have to remove both the link and the link's target. Cleanup is left entirely to the reader.

down

divinity76+yaoiporn at gmail dot com ¶

11 years ago

if you don't want to take care of deleting the file yourself, and you don't need a custom prefix, you can use
$file_location=stream_get_meta_data(tmpfile())['uri'];
file will be created automatically, and deleted automatically on script close (thanks to tmpfile()) i found this useful for CURLOPT_COOKIEFILE (which wants a file location, not a handle)

down

wapmorgan ¶

10 years ago

Notice that tempnam will return NULL (not false) if the second parameter <prefix> isn't transferred:
<?php
var_dump(tempnam(sys_get_temp_dir())); // NULL
?>
also the warning will be generated:
Warning:  tempnam() expects exactly 2 parameters, 1 given in php shell code ...

down

tux ARROBA cenobioracing PUNTO com ¶

18 years ago

Beware that on Windows NT and other windows, if you have, for example, a variable $work_dir with a path to some dir on your document root(or any other dir). Note the following:
<?php
$work_dir = 'C:/some/path/to/document_root/dir';
file_exists($working_dir); // Returns true
is_writable($working_dir); // Returns true
$tempfile = tempnam($working_dir,'img');
//$temfile now contains a system wide temp directory file, like 'C:/WINNT.SBS/img444.tmp' instead of the directory we pass it
//Thats because we need to give I_USR (IIS user) user write permission to $working_dir  although according to the aforementioned functions seemed it already had it...
//If you want to use just the system wide temp directory return by default by tempnam you will also need to give it write permission to I_USR user to be able to write to that file...
?>

down

tomas at slax dot org ¶

14 years ago

Beware: functions are not atomic.  If many processes call the same function at the same time, you may end up with unwanted behavior.



If you need your own variant of tempnam, use something like this:



<?php

   function tempnam_sfx($path, $suffix)

   {

      do

      {

         $file = $path."/".mt_rand().$suffix;

         $fp = @fopen($file, 'x');

      }

      while(!$fp);



      fclose($fp);

      return $file;

   }



   // call it like this:

   $file = tempnam_sfx("/tmp", ".jpg");

?>



You may replace mt_rand() by some other random name generator, if needed.

down

lreilly at lanl dot gov ¶

22 years ago

Be careful with you forward and back slashes. Innocent looking code like this...

$uploaddir = "C:/Program Files/Apache Group/Apache2/htdocs/sasdap/uploads/";
$tempFile = tempnam ($uploaddir, "TMPANAL");
$fp = fopen($tmpfname, "w");
fwrite($fp, $iqdata);
//fclose($fp);

... may show something odd when echoing $tempFile";

i.e. /Program Files/Apache Group/Apache2/htdocs/sasdap/uploads/\TMP3D.tmp
                                                       
Must... remember... to... use... backslashes...

 - Lee P. Reilly

down

Anonymous ¶

12 years ago

tempnam will not create file in unauthorized area.
Meaning you need access permissions to the temp dir ($dir) in order to create a file there.

down

phpdoc at rickbradley dot com ¶

20 years ago

The "newtempnam" recipe provided below (posted by "tempnam" on " 23-Jul-2003 08:56") has at least one race condition.  The while loop checks to make sure that the file in question doesn't exist, and then goes and creates the file.  In between the existence test and the fopen() call there is an opportunity for an attacker to create the file in question.

This is a classic race-condition, and while it seems difficult to exploit there are a number of well-known attacks against this kind of sloppy file creation.

The atomic primitives necessary to implement secure file creation are not available at the language level in PHP.  This further underscores the need for PHP-language developers to rely on the language's security primitives (including tempnam() and tempfile()) instead of rolling their own.

down

dmhouse at gmail dot com ¶

17 years ago

Guillaume Paramelle's comments below are worth underlining: tempnam() will not accept a relative path for its first directory. If you pass it one, it will (on Windows XP at least) create the temporary file in the system temp directory.

The easiest way to convert a relative path to an absolute path is to prepend getcwd():

<?php
$file = tempnam('files/temp', 'tmp'); // Wrong!
$file = tempnam(getcwd() . 'files/tmp', 'tmp') // Right.
?>

down

david at frankieandshadow dot com ¶

6 years ago

Debian 9 Stretch adds private temporary directories, so if you use this function when running as mod_php in Apache expecting that the file can be made available to a third party (e.g. in a shell command or a MariaDB load from temporary file command), it will no longer work: the file will not be visible to other processes, (though the same PHP will be able to read it back in).

Either you need to use the first parameter to put the temporary file somewhere specific (outside the HTML document tree) with permissions such that you can share it with the other party, or change the settings for private tmp, for example:

cp /lib/systemd/system/apache2.service /etc/systemd/system/
# edit /etc/systemd/system/ to change PrivateTmp=true to false
systemctl daemon-reload
service apache2 restart

Choosing a different location is better on a shared server - private tmp files were added for a reason.

This was something that puzzled me for ages when doing a recent OS upgrade.

down

hm2k at php dot net ¶

15 years ago

<?php

function tempdir($dir=false,$prefix='php') {
    $tempfile=tempnam('','');
    if (file_exists($tempfile)) { unlink($tempfile); }
    mkdir($tempfile);
    if (is_dir($tempfile)) { return $tempfile; }
}

/*example*/

echo tempdir();
// returns: /tmp/8e9MLi

?>

down

anthon at piwik dot org ¶

14 years ago

The file created by tempnam() will have file permissions that reflect the current umask applied to the default (e.g., 0600 or -rw-------).  This is the case whether the umask is set before starting the web server process, or set by an earlier call to PHP's umask() function.

For example, if the current umask is 0022, the temporary file is created with permissions 0600 (read/write by owner).

Also, if the current umask is 0222, the temporary file is created with permissions 0400 (read-only by owner).  (This is problematic if your code then tries to open the temporary file for writing.)

It's important to remember that the umask revokes permissions.  In neither of the above examples are the group, other, or execute permissions set.

See:  umask(), chmod().

down

-3

KOmaSHOOTER at gmx dot de ¶

19 years ago

This Example makes a File called "user.txt"
in the dir www.XXXXX.XX/restricted/
<?php
$tmpfname = tempnam($_ENV["DOCUMENT_ROOT"]."/restricted", "FOO");
$handle = fopen($tmpfname, "w");
fwrite($handle, "writing to tempfile");
fclose($handle);

// do here something
//echo($_ENV["DOCUMENT_ROOT"]);
copy($tmpfname,'user.txt');
 ?>

down

-3

Nick Smith ¶

19 years ago

It is worth noting that if the 'dir' that you supply doesn't exist, then it is silently ignored and the system /tmp directory used. At least under Linux, PHP v4.1.2.

I had a script that appeared to work fine with safe mode switched off, but I didn't realise that my 'dir' parameter had a typo (so the files were going in /tmp), and once safe mode was switched on I started getting errors because the rest of the script couldn't read files from the system /tmp folder.

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tempnam

Description

Parameters

Return Values

Changelog

Examples

Notes

See Also

Improve This Page

User Contributed Notes 22 notes