What is the program in linux to open a file with it's proper handler?

 In Linux, the standard command-line utility used to open a file with its preferred or "proper" application (based on its MIME type) is xdg-open.

Part of the xdg-utils package, this tool is desktop-agnostic, meaning it works whether you are using GNOME, KDE, XFCE, or even a basic window manager, provided the underlying desktop environment tools are installed.

---

Using xdg-open

The syntax is straightforward. You simply pass the file path or URL as an argument:

Bash

xdg-open filename.pdf    # Opens in your default PDF viewer
xdg-open image.png       # Opens in your default image viewer
xdg-open https://google.com # Opens in your default web browser

How it works

xdg-open looks at the file's extension and content to determine its MIME type. It then consults the desktop's association files (usually found in /usr/share/applications or ~/.local/share/applications/mimeapps.list) to find which application is registered to handle that type.

Alternatives

Depending on your specific environment, you might also see these commands, though xdg-open is the most portable:

• gio open: The modern replacement for gvfs-open, used primarily in GNOME/Gtk environments.

• kde-open: The specific handler for KDE Plasma environments.

• open: On macOS, this is the equivalent command (on some Linux distros, open is aliased to openvt, which is different).

---

Python Implementation

If you are working in Python and prefer PEP 8 standards, you can invoke this functionality using the subprocess module. This is useful if you want your Python script to trigger the system's default viewer for a generated report or image.

Python

import subprocess
import sys
from typing import List


def open_file_with_default_handler(filepath: str) -> None:
    """
    Open a file using the system's default application.

    Args:
        filepath: The path to the file to be opened.
    """
    try:
        if sys.platform.startswith('linux'):
            subprocess.run(['xdg-open', filepath], check=True)
        elif sys.platform == 'darwin':  # macOS
            subprocess.run(['open', filepath], check=True)
        elif sys.platform == 'win32':  # Windows
            subprocess.run(['start', filepath], shell=True, check=True)
    except subprocess.CalledProcessError as err:
        print(f"Failed to open file: {err}")


if __name__ == "__main__":
    # Example usage
    open_file_with_default_handler("example_document.pdf")

Unit Test

Following your requirement for unittest and type hints:

Python

import unittest
from unittest.mock import patch
import sys


class TestFileHandler(unittest.TestCase):
    """Tests for the open_file_with_default_handler function."""

    @patch('subprocess.run')
    def test_open_file_linux(self, mock_run: unittest.mock.MagicMock) -> None:
        """Test that xdg-open is called correctly on Linux platforms."""
        # Force platform to linux for the test
        with patch('sys.platform', 'linux'):
            from file_opener import open_file_with_default_handler
            test_path: str = "test.txt"
            open_file_with_default_handler(test_path)
            mock_run.assert_called_once_with(['xdg-open', test_path], 
                                             check=True)


if __name__ == '__main__':
    unittest.main()