PHP File Info: filesize(), pathinfo() and finfo

PHP can tell you a lot about a file without opening it.

Size and dates

index.php

PHP

<?php
file_put_contents("report.txt", "Quarterly numbers");

echo filesize("report.txt") . " bytes\n";
echo date("Y", filemtime("report.txt")) === date("Y") ? "modified this year" : "older";

Output

OUTPUT

1
2

17 bytes
modified this year

filesize($file): size in bytes.
filemtime($file): last modified time, as a Unix timestamp.
fileatime() and filectime(): last access and last change of the file’s metadata.

Name, folder and extension

index.php

PHP

<?php
$path = "/var/uploads/2026/photo.final.JPG";

print_r(pathinfo($path));

echo strtolower(pathinfo($path, PATHINFO_EXTENSION));

Output

OUTPUT

Array
(
    [dirname] => /var/uploads/2026
    [basename] => photo.final.JPG
    [extension] => JPG
    [filename] => photo.final
)
jpg

pathinfo() works on a string. It does not look at the real file.

A readable size

index.php

PHP

<?php
function humanSize(int $bytes): string
{
    $units = ["B", "KB", "MB", "GB"];
    $i = 0;

    while ($bytes >= 1024 && $i < count($units) - 1) {
        $bytes /= 1024;
        $i++;
    }

    return round($bytes, 1) . " " . $units[$i];
}

echo humanSize(900) . "\n";
echo humanSize(5242880) . "\n";
echo humanSize(1610612736);

Output

OUTPUT

1
2
3

900 B
5 MB
1.5 GB

The real file type: finfo

The extension is only a name. A file called photo.jpg might contain anything. To find out what the content really is, use the finfo class (the fileinfo extension).

index.php

PHP

<?php
// the smallest valid PNG image
$png = base64_decode("iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg==");
file_put_contents("fake.jpg", $png);   // a PNG pretending to be a JPG

$finfo = new finfo(FILEINFO_MIME_TYPE);

echo $finfo->file("fake.jpg");

Output

OUTPUT

image/png

The name says .jpg, but the content is a PNG. finfo looks at the bytes, so you cannot be fooled by a rename. You will use this in Secure File Uploads.

Image size

index.php

PHP

<?php
$png = base64_decode("iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mNk+M9QDwADhgGAWjR9awAAAABJRU5ErkJggg==");
file_put_contents("tiny.png", $png);

[$width, $height] = getimagesize("tiny.png");

echo "$width x $height";

Output

OUTPUT

1 x 1

getimagesize() also returns false if the file is not a valid image, which makes it a useful extra check.

Clear the file status cache

PHP caches some results (filesize, file_exists) during one script. If the file changes while the script runs, call clearstatcache() before checking again.

lightbulb

Do not trust extensions

Use pathinfo() for the name, and finfo for what the file really is.