popen.py

from subprocess import Popen, PIPE
p = Popen(['tail', '-f', 'popen_test'], stdout=PIPE)
p.stdout.readline() # will block until there is something to be read

# Then just `echo "hello world!" >> popen_test

test_popen.py

#!/bin/usr/env python
'''
Usage:
  pcap_tender.py <feed> <iface> [--debug]

Options:
  -h, --help     Print this screen.
  -v, --version  Print the version
  --debug        Verbose output, and don't actually move anything.

'''

from subprocess import Popen, PIPE
from datetime import datetime
import re

from docopt import docopt


def copy_to_wmd(filename):
    ''' Copy a given file to /wmd
    '''
    pass


def initiate_dumpcap(args):
    ''' start dumpcap with -a duration=<time_remaining_until_5min_marker>
    '''
    pass


def monitor_dumpcap(args):
    ''' start the dumpcap process and monitor the output

    Dumpcap produces the following output while it works. 
    The first two lines when it starts, and the following two when
    it finishes:
    ```
    Capturing on eth1
    File: /data/noc1_04219_20130718114010.pcapng
    Packets captured: 181094
    Packets received/dropped on interface eth1: 181094/64 (100.0%)
    ```
    '''

    c = "tail -f test_process"

    p = Popen(c.split(), stdout=PIPE, stderr=PIPE)

    for line in p.stdout.readlines():
        if re.match("File: ", line) :
            # save filename for currently written file
        if re.match("Packets captured"):
            # we're done with the file
            copy_to_wmd(filename)  # copy freshly created file to wmd


if __name__ == '__main__':
    args = docopt(__doc__, version='PCAP Tender 0.01')
    print(args)