Question

Write a program copyfile that copies one file to another. The file names are specified on the command line. For example, copyfile report. txt report.sav

Short answer

Write a Python script using `shutil.copy` to copy files, handling filenames via command-line arguments.

Step-by-step solution

Understand the Task

We need to create a program that copies a file from one location to another. The program should be able to take the file names (source and destination) as command-line arguments.

Setup the Command-line Tool

We should use a programming language that efficiently supports file handling and command-line operations. Python is suitable due to its simple syntax for these tasks.

Import Necessary Libraries

In Python, to handle file copying, we can use the `shutil` module which provides a method to copy files. ```python import shutil import sys ```

Define the Main Function

Create a `main` function to handle argument parsing and initiate the copy operation. Use `sys.argv` to read command-line arguments. ```python def main(): if len(sys.argv) != 3: print("Usage: copyfile source_file destination_file") return source_file = sys.argv[1] destination_file = sys.argv[2] ```

Perform File Copying

Use `shutil.copy` to copy the contents from the source file to the destination file specified in the command line arguments. ```python try: shutil.copy(source_file, destination_file) print(f"Copied {source_file} to {destination_file}") except IOError as e: print(f"Unable to copy file. {e}") ```

Add the Entry Point

Ensure the program only executes the copy when run directly, not when imported. ```python if __name__ == "__main__": main() ```

Final Implementation

The complete program looks like this: ```python import shutil import sys def main(): if len(sys.argv) != 3: print("Usage: copyfile source_file destination_file") return source_file = sys.argv[1] destination_file = sys.argv[2] try: shutil.copy(source_file, destination_file) print(f"Copied {source_file} to {destination_file}") except IOError as e: print(f"Unable to copy file. {e}") if __name__ == "__main__": main() ```

Key concepts

Command-line Arguments

Command-line arguments are a way in which a user can provide input data to a program directly from the terminal or command prompt when executing the program. In the exercise, these arguments are used to specify the source and destination file names, which are crucial for copying the file.
To capture command-line arguments in a Python script, the `sys` module is used. This module gives you access to `sys.argv`, which is a list in Python that contains the command-line arguments passed to the script. The first element, `sys.argv[0]`, is the script name itself, and the subsequent ones are the additional arguments provided by the user.

• For example, if you run `python copyfile.py file1.txt file2.txt`, `sys.argv` would be `['copyfile.py', 'file1.txt', 'file2.txt']`.
• In our solution, `sys.argv[1]` holds the source file and `sys.argv[2]` is the destination file name.

It is crucial to ensure the user provides the correct number of arguments. If not, the program should give a helpful usage message and halt execution to prevent any errors.

Python Programming

Python is an excellent choice for file handling tasks due to its easy-to-read syntax and powerful library support. The language allows you to execute comprehensive operations with minimal lines of code, which is why it's a preferred choice for scripting.
In the context of the exercise, Python is used due to its simplicity and ability to quickly handle file operations utilizing modules such as `shutil`. Setting up a Python program involves some basic steps which include importation of needed modules and defining functions to handle specific tasks.

• Python programs are usually initiated with a check using `if __name__ == "__main__":` to ensure that code is only executed when the file is run directly and not when it's imported as a module.
• It's also important to implement error handling using `try` and `except` blocks to catch potential mistakes or issues, like an `IOError` if there is a problem accessing a file.

Python's straightforward approach to file operations, coupled with its robust community and documentation, makes it ideal for learning and executing tasks such as file copying.

Shutil Module

The `shutil` module in Python is a high-level file operation module that is specifically used for file copying and removal. In our file copying program, we rely on `shutil.copy`, which simplifies the process of copying files.
The `shutil` module abstracts the complexity of file operations by providing simple functions to perform these tasks. This is particularly useful when performing system-level file operations and automation.

• `shutil.copy(src, dst)`: This function is used to copy the contents of the source file (`src`) to the destination file (`dst`). It takes care of opening, reading, writing, and closing the files efficiently.
• Comprehensive error handling with `shutil`: `shutil.copy` also handles file permissions and raises exceptions if it encounters problems such as non-existent files or permission errors, which can be managed using `try` and `except` blocks.

Shutil makes file handling tasks both powerful and intuitive, making it a convenient choice for tasks like file copying or directory cleanup, ensuring you focus more on the logic rather than the underlying system intricacies.