filemtime

(PHP 4, PHP 5, PHP 7)

filemtime — 取得文件修改时间

说明

int filemtime ( string $filename )

本函数返回文件中的数据块上次被写入的时间，也就是说，文件的内容上次被修改的时间。

参数

filename

文件的路径。

返回值

返回文件上次被修改的时间， 或者在失败时返回 FALSE。时间以 Unix 时间戳的方式返回，可用于 date()。

范例

Example #1 filemtime() 例子

<?php
// outputs e.g.  somefile.txt was last modified: December 29 2002 22:16:23.

$filename = 'somefile.txt';
if (file_exists($filename)) {
    echo "$filename was last modified: " . date ("F d Y H:i:s.", filemtime($filename));
}
?>

错误／异常

失败时抛出E_WARNING警告。

注释

Note:

注意：不同文件系统对时间的判断方法可能是不相同的。

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

User Contributed Notes

Don 13-Aug-2015 03:13
To find the oldest file in a directory :
$directory= "C:\\";

$smallest_time=INF;

$oldest_file='';

if ($handle = opendir($directory)) {

    while (false !== ($file = readdir($handle))) {

        $time=filemtime($directory.'/'.$file);

        if (is_file($directory.'/'.$file)) {

            if ($time < $smallest_time) {
                $oldest_file = $file;
                $smallest_time = $time;
            }
        }
    }
    closedir($handle);
}

echo $oldest_file;
son9ne at gmail dot com 02-Mar-2014 04:58
If you do use:
<?php
$filename = 'somefile.txt';
$fmtime = filemtime($filename);
if (!$fmtime) {
    echo "$filename wurde zuletzt modifiziert:: " . date ("F d Y H:i:s.", $fmtime);
}
?>

Make note that it will throw a warning as the documentation states. While tobias makes a good point for production, when error reporting is off, this can increase your performance over using `file_exists`. However, if error reporting is on and it's writing to a log... this is not the case. Obviously this varies on sever specs and the size of the error log. For most cases, it's still ideal to use the `file_exists` method.
arkadia81 at gmail dot com 04-Oct-2013 10:56
A little amendment to "tobias" post:

Insted of:
$filename = 'somefile.txt';
 $fmtime = filemtime($filename);
 if (!$fmtime) {
     echo "$filename wurde zuletzt modifiziert:: " . date ("F d Y H:i:s.", $fmtime);
}

it should be something like this:
$filename = 'somefile.txt';
 $fmtime = filemtime($filename);
 if ($fmtime != false) {
     echo "$filename wurde zuletzt modifiziert:: " . date ("F d Y H:i:s.", $fmtime);
 }

filemtime() returns false on failure so in the first example it will never display the date modified.
tobias 19-Sep-2013 05:02
The mentioned example:

$filename = 'somefile.txt';
if (file_exists($filename)) {
    echo "$filename wurde zuletzt modifiziert:: " . date ("F d Y H:i:s.", filemtime($filename));
}

works, however is not ideal from a performance point of view of serving static files through PHP, since it basically needs two perform two file system operations (file_exists and filemtime). A more effective way would be to only use filemtime and save the overhead of file_exists using:

$filename = 'somefile.txt';
$fmtime = filemtime($filename);
if (!$fmtime) {
    echo "$filename wurde zuletzt modifiziert:: " . date ("F d Y H:i:s.", $fmtime);
}
nieprzeklinaj at gmail dot com 22-Jan-2013 09:56
Here's a handy little function for smart cache overriding :)
<?php
function img($src, $alt='', $attr='')
{
    if(file_exists($src))
    {
        $lmod = filemtime($src);
        echo '<img src="'.$src.'?lmod='.$lmod.'" alt="'.$alt.'" '.$attr.' />';
    }
}
?>
Will Davies Vasconcelos 17-Feb-2011 07:22
Here is a handy script to create a csv file with file names and the date when files in a given folder were inserted:

<?php
  header("Pragma: public");
  header("Cache-Control: private");
  header("Content-Type: text/csv");
  header("Content-Disposition: attachment; filename=age-of-files.csv");

  $result = array();
  $handle =  opendir(".");
     while ($datei = readdir($handle))
     {
          if (($datei != '.') && ($datei != '..'))
          {
               $file = "./".$datei;
               if (!is_dir($file))
                    $result[] = $file;
          }
     }
     closedir($handle);
  foreach($result as $r)
    if (file_exists($r))
      echo substr($r,2).",".date ("m/d/Y", filemtime($r))."\r\n";
?>
myselfasunder at gmail dot XYZ dot com 31-Oct-2010 11:02
There's a deeply-seated problem with filemtime() under Windows due to the fact that it calls Windows' stat() function, which implements DST (according to this bug: http://bugs.php.net/bug.php?id=40568). The detection of DST on the time of the file is confused by whether the CURRENT time of the current system is currently under DST.

This is a fix for the mother of all annoying bugs:

<?php
function GetCorrectMTime($filePath)
{

    $time = filemtime($filePath);

    $isDST = (date('I', $time) == 1);
    $systemDST = (date('I') == 1);

    $adjustment = 0;

    if($isDST == false && $systemDST == true)
        $adjustment = 3600;
   
    else if($isDST == true && $systemDST == false)
        $adjustment = -3600;

    else
        $adjustment = 0;

    return ($time + $adjustment);
}
?>

Dustin Oprea
erelsgl at gmail dot com 07-Jun-2010 10:08
Cheaper and dirtier way to code a cache:

<?php
$cache_file = 'URI to cache file';
$cache_life = '120'; //caching time, in seconds

$filemtime = @filemtime($cache_file);  // returns FALSE if file does not exist
if (!$filemtime or (time() - $filemtime >= $cache_life)){
    ob_start();
    resource_consuming_function();
    file_put_contents($cache_file,ob_get_flush());
}else{
    readfile($cache_file);
}
?>
dagger80 07-Apr-2010 09:22
Also on 32-bit systems, filemtime() also does not work for files with modification time set beyond Jan 2038. It is the dreaded time_t overflow bug for unix seconds.

On windows you can set the system time to any arbitrary future date, and any new files you created or edited will automatically change to that future date.

If exec isn't permitted for some reason, and if you could access the file via an web url (e.g. http://localhost/yourfile.txt), another workaround is to get the Last-Modified time from the HTTP headers (e.g. get_headers(url) ), and parse it as a DateTime object.

I have tested it and it works for years like 2050 and 3012.
_michael 01-Feb-2010 08:09
While testing on Windows, I noticed that the precision of filemtime is just 1 second.

So if you use clearstatcache() and filemtime() to check if a file has been modified, it might fail to detect the change. The modifications just have to happen within less than a second.

(I ran into this with Apache on Windows XP.)
Nilo 11-Jan-2010 08:01
Cheap and dirty way to code a cache:

<?php
$cache_file = 'URI to cache file';
$cache_life = '120'; //caching time, in seconds

if (!file_exists($cache_file) or (time() - filemtime($cache_file) >= $cache_life)){
    ob_start();
    resource_consuming_function();
    file_put_contents($cache_file,ob_get_flush());
}else{
    readfile($cache_file);
}
?>
james dot schafer at gotalk dot net dot au 16-Dec-2009 10:36
On the Windows system filectime() returns the creation time. To find the changed time use fileatime() or filemtime().
contacto at hardcode dot com dot ar 31-Aug-2009 05:03
when working with swf files (flash animations), there is a nice way to avoid the browser cache. i used to do this by hand, then i used a random number, but with large animations while working online, it gets boring because the server always downloads the whole animation, even if there was no change.
but...

this will do the trick

base.swf?rand=<?php echo filemtime("base.swf") ?>

<embed src="base.swf?rand=<?php echo filemtime("base.swf") ?>" quality="high" pluginspage="http://www.macromedia.com/go/getflashplayer" type="application/x-shockwave-flash" width="1680" height="1050">
Anonymous 20-Aug-2009 12:52
Please note that many of the functions below that people have provided to get files modified after a certain time in a directory will NOT get all files on a Windows operating system.

If you copy and paste any file inside the folder or into the folder from another folder (such as images that may be used but aren't going to be modified right away), the modified time is not updated on these copied files, only the creation time.

You need to use filectime with filemtime to assure you get copied files that aren't modified but are obviously new.
info at daniel-marschall dot de 22-Jun-2009 12:59
It could be useful to determinate the timestamp of the newest file in a directory. (e.g. if you want to find out when the last change was made to your project).

Following function will help you:

<?php

function getAllFiles($directory, $recursive = true) {
     $result = array();
     $handle =  opendir($directory);
     while ($datei = readdir($handle))
     {
          if (($datei != '.') && ($datei != '..'))
          {
               $file = $directory.$datei;
               if (is_dir($file)) {
                    if ($recursive) {
                         $result = array_merge($result, getAllFiles($file.'/'));
                    }
               } else {
                    $result[] = $file;
               }
          }
     }
     closedir($handle);
     return $result;
}

function getHighestFileTimestamp($directory, $recursive = true) {
     $allFiles = getAllFiles($directory, $recursive);
     $highestKnown = 0;
     foreach ($allFiles as $val) {
          $currentValue = filemtime($val);
          if ($currentValue > $highestKnown) $highestKnown = $currentValue;
     }
     return $highestKnown;
}

// Use example

echo 'The newest file has the time stamp:<br>';
echo date('Y-m-d H:i:s', getHighestFileTimestamp('../'));

?>
geeks at geekman dot info 18-Feb-2008 06:01
This is a very handy function for dealing with browser caching. For example, say you have a stylesheet and you want to make sure everyone has the most recent version. You could rename it every time you edit it, but that would be a pain in the ass. Instead, you can do this:

<?php
echo '<link rel="stylesheet" type="text/css" href="style.css?' . filemtime('style.css') . '" />';
?>

Sample output:

<link rel="stylesheet" type="text/css" href="style.css?1203291283" />

By appending a GET value (the UNIX timestamp) to the stylesheet URL, you make the browser think the stylesheet is dynamic, so it'll reload the stylesheet every time the modification date changes.
solarijj at gmail dot com 08-Mar-2007 09:02
To get the modification date of some remote file, you can use the fine function by notepad at codewalker dot com (with improvements by dma05 at web dot de and madsen at lillesvin dot net).

But you can achieve the same result more easily now with stream_get_meta_data (PHP>4.3.0).

However a problem may arise if some redirection occurs. In such a case, the server HTTP response contains no Last-Modified header, but there is a Location header indicating where to find the file. The function below takes care of any redirections, even multiple redirections, so that you reach the real file of which you want the last modification date.

hih,
JJS.

<?php

// get remote file last modification date (returns unix timestamp)
function GetRemoteLastModified( $uri )
{
    // default
    $unixtime = 0;
   
    $fp = fopen( $uri, "r" );
    if( !$fp ) {return;}
   
    $MetaData = stream_get_meta_data( $fp );
       
    foreach( $MetaData['wrapper_data'] as $response )
    {
        // case: redirection
        if( substr( strtolower($response), 0, 10 ) == 'location: ' )
        {
            $newUri = substr( $response, 10 );
            fclose( $fp );
            return GetRemoteLastModified( $newUri );
        }
        // case: last-modified
        elseif( substr( strtolower($response), 0, 15 ) == 'last-modified: ' )
        {
            $unixtime = strtotime( substr($response, 15) );
            break;
        }
    }
    fclose( $fp );
    return $unixtime;
}
?>
Benan Tumkaya (benantumkaya at yahoo) 14-Aug-2006 11:11
Here is a small but handy script that you can use to find which files in your server are modified after a  date/time that you specify. This script will go through all folders in the specified directory recursively and echo the modified files with the last modified date/time...

//Starts Here
//Put here the directory you want to search for. Put / if you want to search your entire domain
$dir='/';

//Put the date you want to compare with in the format of:  YYYY-mm-dd hh:mm:ss
$comparedatestr="2006-08-12 00:00:00";
$comparedate=strtotime($comparedatestr);

//I run the function here to start the search.
directory_tree($dir,$comparedate);

//This is the function which is doing the search...
function directory_tree($address,$comparedate){

 @$dir = opendir($address);

  if(!$dir){ return 0; }
        while($entry = readdir($dir)){
                if(is_dir("$address/$entry") && ($entry != ".." && $entry != ".")){                            
                        directory_tree("$address/$entry",$comparedate);
                }
                 else   {

                  if($entry != ".." && $entry != ".") {
                 
                    $fulldir=$address.'/'.$entry;
                    $last_modified = filemtime($fulldir);
                    $last_modified_str= date("Y-m-d h:i:s", $last_modified);

                       if($comparedate < $last_modified)  {
                          echo $fulldir.'=>'.$last_modified_str;
                          echo "<BR>";
                       }

                 }

            }

      }

}
csnyder at chxo dot com 11-Aug-2006 05:59
If PHP's integer type is only 32 bits on your system, filemtime() will fail on files over 2GB with the warning "stat failed". All stat()-related commands will exhibit the same behavior.

As a workaround, you can call the system's stat command to get the modification time of a file:

On FreeBSD:
$mtime = exec ('stat -f %m '. escapeshellarg ($path));

On Linux:
$mtime = exec ('stat -c %Y '. escapeshellarg ($path));

Thanks to "mpb dot mail at gmail dot com" for his/her similar comment on stat().
dma05 at web dot de 23-Apr-2005 11:25
concerning "notepad at codewalkers dot com"'s code:

this code is pretty neat, but i just wanted to note that using the "HEAD"-method instead of the "GET"-method in the http-request might be preferrable, since then not the whole resource is being downloaded...

http/1.1 definiton snippet:
Section "9.4 HEAD"

 The HEAD method is identical to GET except that the server MUST NOT return a message-body in the response. The metainformation contained in the HTTP headers in response to a HEAD request SHOULD be identical to the information sent in response to a GET request. This method can be used for obtaining metainformation about the entity implied by the request without transferring the entity-body itself. This method is often used for testing hypertext links for validity, accessibility, and recent modification. [...]
-- snippet end ---

the code would then be...:

-- snippet ---
fputs($handle,"HEAD $uri[path] HTTP/1.1\r\nHost: $uri[host]\r\n\r\n");
-- snippet end ---

regards, Magnus
notepad at codewalkers dot com 11-Mar-2005 10:53
i needed the ability to grab the mod time of an image on a remote site. the following is the solution with the help of Joe Ferris.

<?php

function filemtime_remote($uri)
{
    $uri = parse_url($uri);
    $handle = @fsockopen($uri['host'],80);
    if(!$handle)
        return 0;

    fputs($handle,"GET $uri[path] HTTP/1.1\r\nHost: $uri[host]\r\n\r\n");
    $result = 0;
    while(!feof($handle))
    {
        $line = fgets($handle,1024);
        if(!trim($line))
            break;

        $col = strpos($line,':');
        if($col !== false)
        {
            $header = trim(substr($line,0,$col));
            $value = trim(substr($line,$col+1));
            if(strtolower($header) == 'last-modified')
            {
                $result = strtotime($value);
                break;
            }
        }
    }
    fclose($handle);
    return $result;
}
// echo filemtime_remote('http://www.somesite.com/someimage.jpg');

?>
habazi at yahoo dot com 21-Feb-2005 07:13
"this is not (necessarily) correct, the modification time of a directory will be the time of the last file *creation* in a directory (and not in it's sub directories)."

This is not (necessarily) correct either. In *nix the timestamp can be independently set. For example the command "touch directory" updates the timestamp of a directory without file creation.

Also file removal will update the timestamp of a directory.
09-Dec-2004 05:30
A comment below states

  "When using this function to get the modified date of a directory,
   it returns the date of the file in that directory that was last modified."

this is not (necessarily) correct, the modification time of a directory will be the time of the last file *creation* in a directory (and not in it's sub directories).
adam at roomvoter dot com 01-May-2004 10:42
The snippet of code earlier that allows you to delete all files older than 2 weeks uses the function (filemtime) - which checks the original create date of the file (filesystem independent).  You MAY want to use filectime() - that looks at when the file was last changed on YOUR file system.

        if (is_dir("$path") )
        {
           $handle=opendir($path);
           while (false!==($file = readdir($handle))) {
               if ($file != "." && $file != "..") { 
                   $Diff = (time() - filectime("$path/$file"))/60/60/24;
                   if ($Diff > 14) unlink("$path/$file");

               }
           }
           closedir($handle);
        }
wookie at at no-way dot org 14-Sep-2003 11:17
Another little handy tool; to get the most recent modified time from files in a directory. It even does recursive directories if you set the $doRecursive param to true. Based on a file/directory list function I saw somewhere on this site. ;)

function mostRecentModifiedFileTime($dirName,$doRecursive) {
    $d = dir($dirName);
    $lastModified = 0;
    while($entry = $d->read()) {
        if ($entry != "." && $entry != "..") {
            if (!is_dir($dirName."/".$entry)) {
                $currentModified = filemtime($dirName."/".$entry);
            } else if ($doRecursive && is_dir($dirName."/".$entry)) {
                $currentModified = mostRecentModifiedFileTime($dirName."/".$entry,true);
            }
            if ($currentModified > $lastModified){
                $lastModified = $currentModified;
            }
        }
    }
    $d->close();
    return $lastModified;
}
paranoid at dds dot nl 05-Jun-2003 02:43
To get the last modification time of a directory, you can use this:

<pre>
$getLastModDir = filemtime("/path/to/directory/.");
</pre>

Take note on the last dot which is needed to see the directory as a file and to actually get a last modification date of it.

This comes in handy when you want just one 'last updated' message on the frontpage of your website and still taking all files of your website into account.

Regards,
Frank Keijzers
jay at fudge dot org 29-Jun-1999 10:55
If you want this functionality for the parent web page you should use getlastmod()
i.e.
<?php echo "Last modified: ".date( "F d Y H:i:s.", getlastmod() ); ?>
within the included page... i.e. as a commont footer include for all pages
gerardj at home dot com 20-May-1999 05:27
The above code works fine if you place it on each page you want a date stamp on.  I've found that if you place a reference such as filemtime(__FILE__) in an included or required file, that the modification time of the inherited file will be returned, not the time of the file that did the ineriting.