问题:

I'm just learning Python but have about 16 years experience with PERL and PHP.

I'm trying to get the output of ngrep and write it to a log file using Python while also tailing the log file. I've seen some examples online but some seem old and outdated and others use shell=True which is discouraged.

In perl I just use something similar to the following

#!/usr/bin/perl open(NGFH,"ngrep -iW byline $filter"); while ($line = <NGFH>) {     open(LOG,">> /path/to/file.log")     // highlighting, filtering, other sub routine calls     print LOG $line }

I've gotten tail to work but ngrep doesn't. I'd like to be able to run this infinately and output the stream from ngrep to the log file after filtering. I couldn't get the output from ngrep to show in stdout so that's as far as I've gotten. I was expecting to be able to see the data file tail as the log file was updated and see the output from ngrep. For now i was just using bash to run the following.

echo "." >> /path/to/ngrep.log

Thanks!

Here's what I got so far...

Updated This seems to work now. I wouldn't know how to improve on it though.

import subprocess import select import re  log = open('/path/to/ngrep.log','a+',0) print log.name  n = subprocess.Popen(['ngrep', '-iW', 'byline'],\     stdout=subprocess.PIPE,stderr=subprocess.STDOUT) p = select.poll() p.register(n.stdout)  f = subprocess.Popen(['tail','-F','-n','0','/path/to/tailme.log'],\     stdout=subprocess.PIPE,stderr=subprocess.PIPE) p2 = select.poll() p2.register(f.stdout)  def srtrepl(match):     if match.group(0) == 'x.x.x.x':         # do something     if match.group(0) == 'x.x.y.y':         # do something else      return '\033[92m'+ match.group(0) + '\033[0m'  while True:     if p.poll(1):         line = n.stdout.readline()         s = re.compile(r'(8.8.(4.4|8.8)|192.168.[0-9]{1,3}.[0-9]{1,3})' )         print s.sub( srtrepl, line )         log.write(n.stdout.readline())      if p2.poll(1):         print f.stdout.readline().rstrip('\n')

回答1:

To emulate your perl code in Python:

#!/usr/bin/env python3 from subprocess import Popen, PIPE  with Popen("ngrep -iW byline".split() + [filter_], stdout=PIPE) as process, \      open('/path/to/file.log', 'ab') as log_file:     for line in process.stdout: # read b'\n'-separated lines         # highlighting, filtering, other function calls         log_file.write(line)

It starts ngrep process passing filter_ variable and appends the output to the log file while allowing you to modify it in Python. See Python: read streaming input from subprocess.communicate() (there could be buffering issues: check whether ngrep supports --line-buffered option like grep and if you want to tail file.log then pass buffering=1 to open(), to enable line-buffering (only usable in the text-mode) or call log_file.flush() after log_file.write(line)).

You could emulate ngrep in pure Python too.

If you want to read output from several processes concurrently (ngrep, tail in your case) then you need to able to read pipes without blocking e.g., using threads, async.io.

转载请标明出处:How to spawn another process and capture output in python?

文章来源: How to spawn another process and capture output in python?

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