PHP filemtime Function
last modified April 3, 2025
The PHP filemtime function returns the last modification time of a
file as a Unix timestamp. It's useful for caching, file synchronization, and
version control.
Basic Definition
The filemtime function retrieves the time when a file's contents
were last modified. It returns a Unix timestamp (seconds since Unix epoch).
Syntax: filemtime(string $filename): int|false. Returns false on
failure. The timestamp can be formatted with date functions for display.
Basic filemtime Example
This shows the simplest usage of filemtime to get modification time.
<?php
declare(strict_types=1);
$file = "example.txt";
$timestamp = filemtime($file);
if ($timestamp !== false) {
echo "Last modified: " . date("Y-m-d H:i:s", $timestamp);
} else {
echo "Could not get modification time";
}
This gets the modification time of "example.txt" and formats it for display. The strict type declaration ensures type safety in the function's return handling.
Checking File Before Access
Always verify a file exists and is readable before calling filemtime.
<?php
declare(strict_types=1);
$file = "config.ini";
if (file_exists($file) && is_readable($file)) {
$timestamp = filemtime($file);
echo "Last modified: " . date("F d Y H:i:s", $timestamp);
} else {
echo "File not accessible";
}
This example demonstrates proper file checking before attempting to get its modification time. It prevents warnings and handles errors gracefully.
Cache Control Example
filemtime is often used for cache validation in web applications.
<?php
declare(strict_types=1);
$cssFile = "styles.css";
$lastModified = filemtime($cssFile);
header("Last-Modified: " . gmdate("D, d M Y H:i:s", $lastModified) . " GMT");
if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) &&
strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) >= $lastModified) {
header("HTTP/1.1 304 Not Modified");
exit;
}
This sends proper cache headers based on file modification time. Browsers can use this to avoid re-downloading unchanged files, improving performance.
Comparing File Ages
Compare modification times to determine which file is newer.
<?php
declare(strict_types=1);
$file1 = "data.json";
$file2 = "backup.json";
$time1 = filemtime($file1);
$time2 = filemtime($file2);
if ($time1 > $time2) {
echo "$file1 is newer than $file2";
} elseif ($time1 < $time2) {
echo "$file2 is newer than $file1";
} else {
echo "Files were modified at the same time";
}
This compares two files' modification times to determine which is newer. Useful for synchronization tasks or determining which version to use.
Directory Modification Check
Check when files in a directory were last modified by checking each file.
<?php
declare(strict_types=1);
$dir = "uploads/";
$latestTime = 0;
if (is_dir($dir)) {
foreach (scandir($dir) as $file) {
if ($file !== "." && $file !== "..") {
$fileTime = filemtime($dir . $file);
if ($fileTime > $latestTime) {
$latestTime = $fileTime;
}
}
}
}
echo "Newest file modified: " . date("Y-m-d H:i:s", $latestTime);
This scans a directory to find the most recently modified file. Useful for monitoring directories for changes or finding the latest uploaded file.
Best Practices
- Error Handling: Always check if filemtime returns false.
- File Permissions: Ensure script has read access to files.
- Caching: Consider caching results for frequently checked files.
- Time Zones: Be aware of timezone settings when formatting.
Source
This tutorial covered the PHP filemtime function with practical
examples showing its usage in different scenarios.