Description

get os.system output python ?

### How to Get the Output from `os.system()` in Python

When working with Python, you might find yourself needing to execute shell commands and capture their output. However, the `os.system()` function does not return the actual output of the command; instead, it only returns the exit code. This can be limiting if you need the output of the command within your Python script. In this post, we will explore how to capture the output of shell commands in Python and discuss alternatives to `os.system()` that better serve this purpose.

#### Limitations of `os.system()`

The `os.system()` function allows you to run a command through the command shell and returns the exit code. While this can be useful for quick and simple command executions, it does not provide a way to capture the output of the command directly in your Python script.

“`python
import os
exit_code = os.system(‘echo Hello, World!’) # Outputs the string to the terminal but captures nothing in the variable
print(exit_code) # Prints: 0 (the exit code)
“`

#### Why Use Alternatives?

To capture the output of commands, you should use alternatives such as the `subprocess` module. The `subprocess` module provides more powerful facilities for spawning new processes and retrieving their results, making it suitable for more complex use cases.

#### Using the `subprocess` Module

The `subprocess` module supports a variety of functions that allow you to run commands and get the output. Here are some examples:

1. **`subprocess.run()`**

Introduced in Python 3.5, this function is recommended for most use cases. It starts the process, waits for it to complete, and then returns a `CompletedProcess` instance containing the executed arguments, the exit status, and the output of the process.

“`python
import subprocess

result = subprocess.run([‘ls’, ‘-l’], capture_output=True, text=True)
print(result.stdout) # This will print the output of ‘ls -l’.
“`

2. **`subprocess.check_output()`**

This function runs the command and returns the output from `stdout`. If the return code was not zero, it raises a `CalledProcessError`. This method is convenient when you are sure the command will not fail and you need to capture its output.

“`python
import subprocess

output = subprocess.check_output([‘ls’, ‘-l’], text=True)
print(output) # This will print the output of ‘ls -l’.
“`

3. **Using `subprocess.Popen`**

Provides more flexibility and control. This is typically used if you need to handle the output line by line or if you need to interact with the command during its execution.

“`python
import subprocess

process = subprocess.Popen([‘ls’, ‘-l’], stdout=subprocess.PIPE, text=True)
output, error = process.communicate()
print(output) # This will print the output of ‘ls -l’.
“`

#### Why Not `os.popen()`?

`os.popen()` can be used to create a pipe to or from a process. This function is similar to `popen2.popen3()`, and is mostly maintained for backward compatibility. Since the introduction of the `subprocess` module, this function has been largely deprecated in favor of `subprocess.run()`, `subprocess.call()`, `subprocess.check_call()`, and `subprocess.check_output()`.

#### Conclusion

While `os.system()` is useful for basic command execution, it falls short when you need to capture the output of a command. Using the `subprocess` module, you can effectively run shell commands and capture their output, exit codes, and errors, making your Python script more powerful and flexible.

If you have any questions or need further clarification, feel free to ask. Happy coding!

*Sources and Further Reading:*
– [Stack Overflow – How to get the output from os.system()](https://stackoverflow.com/questions/34431673/how-to-get-the-output-from-os-system)
– [Roel Peters – Python: execute shell commands (and get the output) with the os package](https://www.roelpeters.be/python-execute-shell-commands-and-get-the-output/)
– [ITCodar – Return Value of X = Os.System](https://www.itcodar.com/python/return-value-of-x-os-system.html)