How to Tee Subprocess Output to Files and Terminal Simultaneously in Python?

Teeing Subprocess Output to Files and Terminal Simultaneously

Python's subprocess.call() method allows you to execute external commands. However, by default, the output is directed to the terminal. This article addresses the question of how to simultaneously write the output to both files and the terminal.

The answer lies in using the Popen() function directly, which offers greater control over the execution process. By specifying stdout=PIPE, you can read from the process's stdout stream. To achieve the desired behavior, follow these steps:

1. Create a Tee Function: Define a function that reads from an input file and writes it to multiple output files. This function runs in a separate thread, ensuring that the main process is not blocked.
2. Use Tee Function in Teed_Call Function: Create a wrapper function named teed_call() that calls Popen() with stdout=PIPE and stderr=PIPE. It uses the tee() function to write the stdout and stderr streams to both files and the terminal.
3. Execute Commands with Teeing: Call teed_call() with the desired command arguments and specify the output files using the stdout and stderr parameters.
4. Wait for Output Completion: After executing the command, join the thread created by the tee() function to ensure that all output is written before continuing.

The code example provided in the answer demonstrates how to use the teed_call() function to tee the stdout and stderr streams of various commands, including cat, echo, and gcc.

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