Subprocess.Popen: cloning stdout and stderr both to terminal and variables

Subprocess.Popen: cloning stdout and stderr both to terminal and variables

You can use the subprocess.Popen class in Python to run an external command and capture both its standard output (stdout) and standard error (stderr) streams, while also printing them to the terminal. To achieve this, you can redirect both stdout and stderr to subprocess.PIPE and then read and display them while storing their contents in variables. Here's an example of how you can do this:

import subprocess # Define the command to run (e.g., 'ls' in this example) command = ['ls', '-l'] # Create a subprocess, redirecting both stdout and stderr to pipes process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True) # Initialize variables to store the output and error messages stdout_content = "" stderr_content = "" # Read and print stdout and stderr while capturing their content while True: # Read a line from stdout stdout_line = process.stdout.readline() # Read a line from stderr stderr_line = process.stderr.readline() # Check if both stdout and stderr have reached the end if not stdout_line and not stderr_line: break # Print stdout line to the terminal if stdout_line: print(f"STDOUT: {stdout_line}", end="") # Print stderr line to the terminal if stderr_line: print(f"STDERR: {stderr_line}", end="") # Append stdout and stderr lines to their respective variables stdout_content += stdout_line stderr_content += stderr_line # Wait for the process to finish process.wait() # Print the exit code of the process print(f"Exit Code: {process.returncode}") # You can now access the captured stdout and stderr content in your variables print("Captured STDOUT:") print(stdout_content) print("Captured STDERR:") print(stderr_content)

In this example, we run the ls -l command and redirect both stdout and stderr to pipes. We then continuously read from these pipes line by line, printing the output to the terminal and appending it to the stdout_content and stderr_content variables. Finally, we wait for the process to finish, print its exit code, and display the captured stdout and stderr content.

You can replace the command variable with the specific command you want to run.

Examples

  1. How to capture stdout and stderr in variables while also printing to terminal with Python subprocess?

    • Description: This code snippet demonstrates capturing both stdout and stderr into separate variables while simultaneously displaying them on the terminal.
    • Code:
      import subprocess import sys process = subprocess.Popen( ['ls', '-l'], # Replace with your command stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True ) stdout, stderr = [], [] for line in process.stdout: sys.stdout.write(line) # Print to terminal stdout.append(line) # Capture in variable for line in process.stderr: sys.stderr.write(line) # Print to terminal stderr.append(line) # Capture in variable

  2. How to clone subprocess output to console and variable simultaneously in Python?

    • Description: This code snippet shows how to clone both stdout and stderr to console and capture them in a variable.
    • Code:
      import subprocess import sys process = subprocess.Popen( ['echo', 'Hello, World!'], # Replace with your command stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True ) stdout, stderr = [], [] while process.poll() is None: out = process.stdout.readline() if out: sys.stdout.write(out) # Print to terminal stdout.append(out) # Capture in variable err = process.stderr.readline() if err: sys.stderr.write(err) # Print to terminal stderr.append(err) # Capture in variable

  3. How to read subprocess output line by line in Python and display it in terminal while storing it in a list?

    • Description: This snippet reads stdout and stderr line-by-line, displaying them in the terminal and storing them in lists.
    • Code:
      import subprocess import sys process = subprocess.Popen( ['ping', '-c', '3', 'google.com'], # Replace with your command stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True ) stdout_lines, stderr_lines = [], [] for line in process.stdout: sys.stdout.write(line) # Print to terminal stdout_lines.append(line) # Store in list for line in process.stderr: sys.stderr.write(line) # Print to terminal stderr_lines.append(line) # Store in list

  4. How to simultaneously write subprocess output to a variable and print to console in Python?

    • Description: This example writes subprocess output to a variable and prints it to the console at the same time.
    • Code:
      import subprocess import sys process = subprocess.Popen( ['date'], # Replace with your command stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True ) stdout_content = [] stderr_content = [] # Capture stdout and stderr while printing them for stdout_line in iter(process.stdout.readline, ''): sys.stdout.write(stdout_line) # Print to console stdout_content.append(stdout_line) # Store in variable for stderr_line in iter(process.stderr.readline, ''): sys.stderr.write(stderr_line) # Print to console stderr_content.append(stderr_line) # Store in variable

  5. How to keep subprocess output in a variable and display it to terminal concurrently in Python?

    • Description: This code snippet keeps subprocess output in a variable while also displaying it to the terminal.
    • Code:
      import subprocess import sys process = subprocess.Popen( ['ls', '-l'], # Replace with your command stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True ) stdout_data, stderr_data = [], [] for stdout_line in process.stdout: sys.stdout.write(stdout_line) # Display to terminal stdout_data.append(stdout_line) # Store in variable for stderr_line in process.stderr: sys.stderr.write(stderr_line) # Display to terminal stderr_data.append(stderr_line) # Store in variable

  6. How to display subprocess output in real-time in terminal while storing in a variable?

    • Description: This code demonstrates how to display subprocess output in real-time while also storing it in a variable.
    • Code:
      import subprocess import sys process = subprocess.Popen( ['tail', '-f', '/var/log/syslog'], # Example command, replace with yours stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True ) stdout_content = [] stderr_content = [] while process.poll() is None: stdout_line = process.stdout.readline() if stdout_line: sys.stdout.write(stdout_line) # Display in real-time stdout_content.append(stdout_line) # Store in variable stderr_line = process.stderr.readline() if stderr_line: sys.stderr.write(stderr_line) # Display in real-time stderr_content.append(stderr_line) # Store in variable

  7. How to collect stdout and stderr from subprocess and show in console with Python?

    • Description: This snippet collects stdout and stderr and displays them in the console while also saving to a variable.
    • Code:
      import subprocess import sys process = subprocess.Popen( ['cat', '/etc/hosts'], # Example command, replace with yours stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True ) collected_stdout = [] collected_stderr = [] for stdout_line in process.stdout: sys.stdout.write(stdout_line) # Display in console collected_stdout.append(stdout_line) # Store in variable for stderr_line in process.stderr: sys.stderr.write(stderr_line) # Display in console collected_stderr.append(stderr_line) # Store in variable

  8. How to run a Python subprocess and capture stdout while printing to terminal?

    • Description: This example demonstrates how to run a subprocess and capture stdout while printing it to the terminal in real-time.
    • Code:
      import subprocess import sys process = subprocess.Popen( ['uname', '-a'], # Replace with your command stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True ) stdout_output = [] while process.poll() is None: line = process.stdout.readline() if line: sys.stdout.write(line) # Print to terminal stdout_output.append(line) # Store in variable

  9. How to execute a command in Python subprocess and capture stdout while printing to console?

    • Description: This code snippet shows how to execute a command in Python subprocess and capture stdout, printing it to the console in real-time.
    • Code:
      import subprocess import sys process = subprocess.Popen( ['df', '-h'], # Replace with your command stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True ) stdout_captured = [] while process.poll() is None: output = process.stdout.readline() if output: sys.stdout.write(output) # Print to console stdout_captured.append(output) # Store in variable

  10. How to display both stdout and stderr to console and capture in variables with Python subprocess?

    • Description: This snippet demonstrates displaying both stdout and stderr to the console and capturing them into variables.
    • Code:
      import subprocess import sys process = subprocess.Popen( ['git', 'status'], # Replace with your command stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True ) stdout_list = [] stderr_list = [] for stdout_line in iter(process.stdout.readline, ''): sys.stdout.write(stdout_line) # Display in console stdout_list.append(stdout_line) # Store in variable for stderr_line in iter(process.stderr.readline, ''): sys.stderr.write(stderr_line) # Display in console stderr_list.append(stderr_line) # Store in variable

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