What is the regex for file extension?

The regex pattern for file extension is `\.[a-zA-Z0-9]+$`. This pattern validates file extension at the end of a filename.

How do I use this regex in JavaScript?

In JavaScript, create the regex with `const regex = /\.[a-zA-Z0-9]+$/;` and test with `regex.test(yourValue)`. It returns `true` if the value matches.

How do I use this regex in Python?

In Python, use `import re; re.match(r'\.[a-zA-Z0-9]+$', value)`. The raw string prefix (`r`) prevents Python from interpreting backslashes as escape characters.

Is this regex case-sensitive?

By default, yes. To make it case-insensitive, add the `i` flag in JavaScript (`/\.[a-zA-Z0-9]+$/i`) or use `re.IGNORECASE` in Python.

Regex for File Extension

Regex Pattern

\.[a-zA-Z0-9]+$

File extension at the end of a filename

Quick Answer

The regex pattern for file extension is `\.[a-zA-Z0-9]+$`. File extension at the end of a filename. This works in JavaScript, Python, Ruby, PHP, Java, and most regex engines that support PCRE syntax.

Test Examples

Input	Result
image.jpg	✓ Matches
document.pdf	✓ Matches
archive.tar.gz	✓ Matches
filename	✗ No match
no.dot at end	✗ No match

Code Examples

javascript

const regex = /\.[a-zA-Z0-9]+$/;
const isValid = regex.test(value);

python

import re
pattern = r'\.[a-zA-Z0-9]+$'
if re.match(pattern, value):
    print("valid")

ruby

pattern = /\.[a-zA-Z0-9]+$/
if value =~ pattern
  puts "valid"
end

php

if (preg_match('/\.[a-zA-Z0-9]+$/', $value)) {
    echo "valid";
}

java

String pattern = "\\.[a-zA-Z0-9]+$";
boolean isValid = value.matches(pattern);

Frequently Asked Questions

Related Regex Patterns

Image File Extension

Common image file extensions

Video File Extension

Common video file extensions

Absolute Unix Path

Absolute filesystem path starting with /

Windows File Path

Windows absolute file path (C:\folder\file.txt)

Unix File Path

Unix absolute file path (must have at least one path component)

Filename with Extension

Filename with at least one extension