clearstatcache

(PHP 4, PHP 5)

clearstatcache — Clears file status cache

Description

void clearstatcache ([ bool $clear_realpath_cache = false [, string $filename ]] )

When you use stat(), lstat(), or any of the other functions listed in the affected functions list (below), PHP caches the information those functions return in order to provide faster performance. However, in certain cases, you may want to clear the cached information. For instance, if the same file is being checked multiple times within a single script, and that file is in danger of being removed or changed during that script's operation, you may elect to clear the status cache. In these cases, you can use the clearstatcache() function to clear the information that PHP caches about a file.

You should also note that PHP doesn't cache information about non-existent files. So, if you call file_exists() on a file that doesn't exist, it will return FALSE until you create the file. If you create the file, it will return TRUE even if you then delete the file. However unlink() clears the cache automatically.

Note:
This function caches information about specific filenames, so you only need to call clearstatcache() if you are performing multiple operations on the same filename and require the information about that particular file to not be cached.

Affected functions include stat(), lstat(), file_exists(), is_writable(), is_readable(), is_executable(), is_file(), is_dir(), is_link(), filectime(), fileatime(), filemtime(), fileinode(), filegroup(), fileowner(), filesize(), filetype(), and fileperms().

Parameters

clear_realpath_cache: Whether to clear the realpath cache or not.
filename: Clear the realpath and the stat cache for a specific filename only; only used if clear_realpath_cache is TRUE.

Return Values

No value is returned.

Changelog

Version	Description
5.3.0	Added optional `clear_realpath_cache` and `filename` parameters.

Examples

Example #1 clearstatcache() example


<?php
$file = 'output_log.txt';

function get_owner($file)
{
    $stat = stat($file);
    $user = posix_getpwuid($stat['uid']);
    return $user['name'];
}

$format = "UID @ %s: %s\n";

printf($format, date('r'), get_owner($file));

chown($file, 'ross');
printf($format, date('r'), get_owner($file));

clearstatcache();
printf($format, date('r'), get_owner($file));
?>

The above example will output something similar to:

UID @ Sun, 12 Oct 2008 20:48:28 +0100: root
UID @ Sun, 12 Oct 2008 20:48:28 +0100: root
UID @ Sun, 12 Oct 2008 20:48:28 +0100: ross

add a note User Contributed Notes clearstatcache - [2 notes]

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-1

matt_m at me dot com ¶

1 year ago


unlink() does not clear the cache if you are performing file_exists() on a remote file like:





<?php


if (file_exists("ftp://ftp.example.com/somefile"))


?>





In this case, even after you unlink() successfully, you must call clearstatcache().





<?php


unlink("ftp://ftp.example.com/somefile");


clearstatcache();


?>





file_exists() then properly returns false.

down

-5

markandrewslade at gmail dot com ¶

3 years ago


On Linux, a forked process inherits a copy of the parent's cache, but after forking the two caches do not impact each other.  The snippet below demonstrates this by creating a child and confirming outdated (cached) information, then clearing the cache, and getting new information.



<?php



function report($directory, $prefix = '') { printf('%sDoes %s exist?  PHP says "%s"'. PHP_EOL, $prefix, $directory, is_dir($directory) ? 'yes' : 'no'); }

$target = './delete-me-before-running-statcache';



if (is_dir($target)) {

    die("Delete $target before running.\n");

}



echo "Creating $target.\n";

mkdir($target) || die("Unable to create $target.\n");

report($target); // is_dir($target) is now cached as true



echo "Unlinking $target.\n";

rmdir($target) || die("Unable to unlink $target.\n");



// This will say "yes", which is old (inaccurate) information.

report($target);



if (($pid = pcntl_fork()) === -1) { die("Failed to pcntl_fork.\n"); }

elseif ($pid === 0) {

    // child

    report($target, '<<child>> ');

    echo "<<child>> Clearing stat cache.\n";

    clearstatcache();

    report($target, '<<child>> ');

} else {

    // parent

    sleep(2); // move this to the child block to reverse the test.

    report($target, '<<<parent>> ');

    clearstatcache();

    report($target, '<<<parent>> ');

}



?>

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