File Path Validation Regex (Windows)

Validate Windows file paths with drive letter, backslashes, and proper filename characters using regex pattern.

Pattern Breakdown

^[a-zA-Z]:\\(?:[^\\/:*?"<>|\r\n]+\\)*[^\\/:*?"<>|\r\n]*$

Components

Character Classes

• [a-zA-Z] - Drive letter: A-Z (case-insensitive)
• [^\\/:*?"<>|\r\n] - Valid path characters (negated class):
  • \ - Not backslash
  • / - Not forward slash
  • : - Not colon (except drive letter)
  • * - Not asterisk
  • ? - Not question mark
  • " - Not double quote
  • < - Not less than
  • > - Not greater than
  • | - Not pipe
  • \r\n - Not carriage return or newline

Examples

Valid:

• C:\Users\Documents\file.txt
• D:\Program Files\App\config.json
• C:\Windows\System32\
• E:\data\folder\
• A:\test.txt

Invalid:

• C:Users\Documents\file.txt (missing root backslash)
• C:\Users\Documents\file*.txt (asterisk not allowed)
• C:\Users\Documents\file?.txt (question mark not allowed)
• C:\Users\Documents\file<name>.txt (angle brackets not allowed)
• C:\Users\Documents\file|name.txt (pipe not allowed)
• /Users/Documents/file.txt (Unix-style path)
• C:/Users/Documents/file.txt (forward slashes)

Implementation

JavaScript

const windowsPathRegex = /^[a-zA-Z]:\\(?:[^\\/:*?"<>|\r\n]+\\)*[^\\/:*?"<>|\r\n]*$/;
windowsPathRegex.test('C:\\Users\\Documents\\file.txt'); // true
windowsPathRegex.test('D:\\Program Files\\App\\config.json'); // true
windowsPathRegex.test('C:\\Users\\Documents\\file*.txt'); // false (invalid char)
windowsPathRegex.test('C:Users\\Documents\\file.txt'); // false (missing backslash)

Python

import re
windows_path_regex = r'^[a-zA-Z]:\\(?:[^\\/:*?"<>|\r\n]+\\)*[^\\/:*?"<>|\r\n]*$'
bool(re.match(windows_path_regex, r'C:\Users\Documents\file.txt'))  # True
bool(re.match(windows_path_regex, r'D:\Program Files\App\config.json'))  # True
bool(re.match(windows_path_regex, r'C:\Users\Documents\file*.txt'))  # False (invalid char)

Go

windowsPathRegex := regexp.MustCompile(`^[a-zA-Z]:\\(?:[^\\/:*?"<>|\r\n]+\\)*[^\\/:*?"<>|\r\n]*$`)
windowsPathRegex.MatchString(`C:\Users\Documents\file.txt`) // true
windowsPathRegex.MatchString(`D:\Program Files\App\config.json`) // true
windowsPathRegex.MatchString(`C:\Users\Documents\file*.txt`) // false (invalid char)

Limitations

1. No UNC paths: Doesn't support \\server\share\path format
2. No relative paths: Only absolute paths with drive letter
3. No long path support: Doesn't handle \\?\ long path prefix
4. No reserved names: Doesn't check for reserved names like CON, PRN, AUX
5. Format only: Validates format, not actual file existence

When to Use

• Windows file path format validation
• File upload validation on Windows systems
• Path sanitization
• When you need to ensure valid Windows path format
• File system operations on Windows

For production, consider:

• Supporting UNC paths if needed
• Supporting relative paths
• Checking for reserved Windows filenames
• Validating path length limits (MAX_PATH = 260 chars)
• Using OS-specific path validation libraries