What is the regex for filename with extension?

The regex pattern for filename with extension is `^[a-zA-Z0-9][a-zA-Z0-9._-]*\.[a-zA-Z0-9]+$`. This pattern validates filename with at least one extension.

How do I use this regex in JavaScript?

In JavaScript, create the regex with `const regex = /^[a-zA-Z0-9][a-zA-Z0-9._-]*\.[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][a-zA-Z0-9._-]*\.[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][a-zA-Z0-9._-]*\.[a-zA-Z0-9]+$/i`) or use `re.IGNORECASE` in Python.

Regex for Filename with Extension

Regex Pattern

^[a-zA-Z0-9][a-zA-Z0-9._-]*\.[a-zA-Z0-9]+$

Filename with at least one extension

Quick Answer

The regex pattern for filename with extension is `^[a-zA-Z0-9][a-zA-Z0-9._-]*\.[a-zA-Z0-9]+$`. Filename with at least one extension. This works in JavaScript, Python, Ruby, PHP, Java, and most regex engines that support PCRE syntax.

Test Examples

Input	Result
file.txt	✓ Matches
my-document.pdf	✓ Matches
image.tar.gz	✓ Matches
app.min.js	✓ Matches
.hidden	✗ No match
noextension	✗ No match
/path/file.txt	✗ No match

Code Examples

javascript

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

python

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

ruby

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

php

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

java

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

Frequently Asked Questions

Related Regex Patterns

File Extension

File extension at the end of a filename

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)