Orchestrating External Commands: A Python Subprocess Challenge

This challenge focuses on utilizing Python's subprocess module to interact with external commands and processes. Understanding how to execute external programs and capture their output is crucial for tasks like system administration, automation, and integrating with other tools. You'll be building a script that executes commands, handles errors, and parses output.

Problem Description

You are tasked with creating a Python script that can execute arbitrary shell commands and return their output (both standard output and standard error) in a structured format. The script should accept a list of commands as input and execute them sequentially. For each command, it should:

1. Execute the command using subprocess.run().
2. Capture both standard output (stdout) and standard error (stderr).
3. Check the return code of the command. If the return code is non-zero (indicating an error), raise a subprocess.CalledProcessError exception with a descriptive message including the command and the return code.
4. Return a dictionary containing the following keys for each command:
   • command: The command that was executed (as a string).
   • stdout: The standard output of the command (as a string).
   • stderr: The standard error of the command (as a string).
   • returncode: The return code of the command (as an integer).

The script should handle potential errors gracefully and provide informative error messages.

Examples

Example 1:

Input: ["ls -l", "pwd"]
Output:
[
    {
        "command": "ls -l",
        "stdout": "total 4\n-rw-r--r-- 1 user user    0 Oct 26 10:00 file1.txt\n",
        "stderr": "",
        "returncode": 0
    },
    {
        "command": "pwd",
        "stdout": "/home/user/project",
        "stderr": "",
        "returncode": 0
    }
]
Explanation: The script executes "ls -l" and "pwd" sequentially.  It captures their respective outputs and return codes, storing them in a dictionary for each command.

Example 2:

Input: ["ls -l non_existent_file", "pwd"]
Output:
[
    {
        "command": "ls -l non_existent_file",
        "stdout": "",
        "stderr": "ls: cannot access 'non_existent_file': No such file or directory\n",
        "returncode": 2
    },
    {
        "command": "pwd",
        "stdout": "/home/user/project",
        "stderr": "",
        "returncode": 0
    }
]
Explanation: The first command fails because the file doesn't exist. The script captures the error message and the non-zero return code. The second command succeeds as usual.

Example 3: (Edge Case - Empty Command List)

Input: []
Output: []
Explanation: If the input list is empty, the script should return an empty list.

Constraints

• The input will be a list of strings, where each string represents a shell command.
• Commands can contain spaces and special characters.
• The script must handle potential FileNotFoundError exceptions if a command is not found on the system. In this case, raise a subprocess.CalledProcessError with a descriptive message.
• The script should be reasonably efficient. Avoid unnecessary overhead.
• The shell=True argument to subprocess.run is not allowed due to security concerns. Commands should be passed as a list of arguments.

Notes

• Consider using subprocess.run() with capture_output=True to simplify capturing stdout and stderr.
• Remember to decode the byte strings returned by capture_output=True into strings using .decode().
• Think about how to handle errors gracefully and provide informative error messages to the user.
• The order of commands in the input list is important; they should be executed sequentially.
• The script should be robust and handle various input scenarios, including empty command lists and commands that fail.