How to Execute Multiple `cat | zgrep` Commands in Parallel with Python?

Python: Executing Cat Subprocess in Parallel

This script aims to run multiple cat | zgrep commands on a remote server, and capture their outputs individually for further processing. However, the current implementation executes these commands sequentially, which hinders performance.

To address this issue, we can leverage the power of parallelism in Python. By modifying the code as follows, we can execute the subprocess calls in parallel while still maintaining the ability to collect the output for each command individually:

<code class="python">import asyncio
import sys
from subprocess import Popen, PIPE, STDOUT

# Run commands in parallel
processes = [Popen('ssh remote_host cat files_to_process | zgrep --mmap "regex"',
                     shell=True, stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True)
              for _ in range(5)]

# Collect outputs in parallel
def get_lines(process):
    return process.communicate()[0].splitlines()

outputs = [get_lines(process) for process in processes]</code>

This updated code utilizes the Process class from the subprocess module to create subprocesses for each command. It then employs the communicate method to capture the output from each process. By providing an empty string as the input to the stdin parameter, we can specify that no input should be sent to the subprocess.

The script also demonstrates how to use a list comprehension to create a list of processes and a list of outputs concurrently. This approach offers a simpler and more concise implementation compared to using multiprocessing or threading.

Furthermore, the script employs the close_fds parameter to ensure that the file descriptors for the child processes are closed after they have been used. This helps prevent potential resource leaks or errors when the subprocesses are executed in parallel.

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