How to Get a File Extension in PHP

By the end of this page, you will understand how file extensions are typically extracted in PHP, why pathinfo() is usually the best choice, how it behaves with edge cases, and when you should avoid relying on extensions alone for file validation.

In PHP, a file extension is usually the part of a filename after the last dot. For example, the extension of photo.jpg is jpg.

The main concept behind this question is string parsing for file paths, but in PHP there is already a built-in function designed for this job: pathinfo().

$extension = pathinfo($filename, PATHINFO_EXTENSION);

This matters because:

• it is clearer than manual string slicing
• it is built into PHP and intended for working with paths
• it handles common filename cases better than many custom solutions
• it makes your code easier to read and maintain

A key practical point: a file extension is just part of the filename. It does not guarantee the actual file type. For example, virus.jpg.exe and photo.jpg are very different files even though both contain .jpg somewhere. In real applications, extensions are helpful for display and simple checks, but not enough for security-sensitive validation.

Think of a filename like a label on a box:

• report.pdf → the label says it is a PDF
• image.png → the label says it is a PNG

The extension is just the last tag after the final dot.

pathinfo() is like asking PHP: "Please break this path into its known parts for me."

Instead of manually cutting the string with knives like substr(), explode(), or regular expressions, you use the tool made specifically for filenames.

The most common and recommended syntax is:

$extension = pathinfo($filename, PATHINFO_EXTENSION);

Basic example

<?php
$filename = 'document.pdf';
$extension = pathinfo($filename, PATHINFO_EXTENSION);

echo $extension; // pdf

PHP looks at the path and returns the part after the last dot.

Example with a full path

<?php
$filename = '/var/www/uploads/photo.jpg';
$extension = pathinfo($filename, PATHINFO_EXTENSION);

echo $extension; // jpg

Example with no extension

<?php
$filename = 'README';
$extension = pathinfo($filename, PATHINFO_EXTENSION);

(); 

Consider this example:

<?php
$filename = 'backup.archive.tar.gz';
$extension = pathinfo($filename, PATHINFO_EXTENSION);

echo $extension;

Step by step:

1. $filename is set to 'backup.archive.tar.gz'.
2. pathinfo($filename, PATHINFO_EXTENSION) examines the filename.
3. PHP finds the last dot in the string.
4. Everything after that last dot is treated as the extension.
5. The result is 'gz'.
6. echo $extension; prints gz.

So even though the filename contains multiple dots, PHP returns only the final extension.

Another trace

<?php
$filename = 'notes.txt';
$extension = pathinfo($filename, PATHINFO_EXTENSION);

Execution:

• filename is

Getting a file extension is common in many PHP applications.

File uploads

You may want to check whether a user uploaded something that looks like an image:

<?php
$allowed = ['jpg', 'jpeg', 'png', 'gif'];
$ext = strtolower(pathinfo($_FILES['upload']['name'], PATHINFO_EXTENSION));

if (!in_array($ext, $allowed, true)) {
    echo 'Unsupported file type.';
}

Naming downloaded files

You might generate a new filename while preserving the original extension:

<?php
$ext = pathinfo($originalName, PATHINFO_EXTENSION);
$newName = uniqid('file_', true) . '.' . $ext;

Displaying file type labels

In real projects, developers usually use pathinfo() together with a few common patterns.

1. Normalize the extension

<?php
$ext = strtolower(pathinfo($filename, PATHINFO_EXTENSION));

This avoids bugs caused by JPG vs jpg.

2. Use guard clauses for validation

<?php
$ext = strtolower(pathinfo($filename, PATHINFO_EXTENSION));

if ($ext === '') {
    throw new InvalidArgumentException('The file has no extension.');
}

This fails early and keeps the rest of the code simpler.

3. Check against an allowlist

<?php
$allowed = ['pdf', 'docx', 'txt'];
$ext = ((, PATHINFO_EXTENSION));

 (!(, , )) {
      ();
}

1. Using explode() directly inside end()

You may see this pattern:

<?php
$ext = end(explode('.', $filename));

This is problematic because it is less readable and can lead to warnings or poor style depending on PHP version and context.

A better version is:

<?php
$ext = pathinfo($filename, PATHINFO_EXTENSION);

2. Assuming every filename has an extension

Broken assumption:

<?php
$filename = 'README';
$ext = pathinfo($filename, PATHINFO_EXTENSION);
echo $ext; // empty string

Avoid this by checking for an empty result.

3. Trusting the extension for security

Broken approach:

// Recommended way
$ext = pathinfo($filename, PATHINFO_EXTENSION);

// Common real-world version
$ext = strtolower(pathinfo($filename, PATHINFO_EXTENSION));

Rules to remember

• The extension is the part after the last dot.
• pathinfo(..., PATHINFO_EXTENSION) returns a string.
• If there is no extension, it returns an empty string.
• Normalize with strtolower() if you need case-insensitive checks.
• Do not trust extensions alone for upload security.

Examples

pathinfo('photo.jpg', PATHINFO_EXTENSION);      // jpg
pathinfo('archive.tar.gz', PATHINFO_EXTENSION); // gz
pathinfo('README', PATHINFO_EXTENSION);         // ''

Safe validation pattern

<?php
$allowed = ['jpg', 'png', ];
 = ((, PATHINFO_EXTENSION));

 ( ===  || !(, , )) {
    
}

What is the best way to get a file extension in PHP?

Use pathinfo($filename, PATHINFO_EXTENSION). It is the clearest built-in solution for working with file paths.

Does pathinfo() return the dot too?

No. It returns only the extension text, such as jpg, not .jpg.

What happens if a file has no extension?

pathinfo($filename, PATHINFO_EXTENSION) returns an empty string.

How do I make extension checks case-insensitive?

Convert the result to lowercase:

$ext = strtolower(pathinfo($filename, PATHINFO_EXTENSION));

What about filenames with multiple dots like archive.tar.gz?

pathinfo() returns only the final part: gz.

Is checking the extension enough for file upload security?

No. A filename can be changed easily. For secure validation, also inspect the file's MIME type or contents.

Should I use split() to get the extension?

• pathinfo() — the built-in PHP function for extracting path parts like directory, basename, filename, and extension.
• string functions in PHP — useful when you need custom parsing logic beyond standard path handling.
• file uploads in PHP — extensions are commonly checked during upload validation.
• MIME type validation — more reliable than extensions when verifying actual file type.
• basename() — helpful when working with filenames extracted from full paths.
• input validation — important when accepting filenames from users or external systems.