Command line arguments/pipe sniffer

#!/usr/bin/python2
import os
import sys
import fcntl
import subprocess
import select

f = open('/tmp/sendmail.args', 'a')
f.write('-->>> ' + ' '.join(sys.argv) + '\n')
f.flush()

p = subprocess.Popen(['/usr/sbin/sendmail.backup'] + sys.argv[1:], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)

def setNonBlocking(fd):
    flags = fcntl.fcntl(fd, fcntl.F_GETFL)
    flags = flags | os.O_NONBLOCK
    fcntl.fcntl(fd, fcntl.F_SETFL, flags)

setNonBlocking(sys.stdin.fileno())
setNonBlocking(p.stdout.fileno())
setNonBlocking(p.stderr.fileno())

while True:
    rr, _, _ = select.select([sys.stdin, p.stdout, p.stderr], [], [])

    for r in rr:
        data = r.read()

        if not data:
            exit(0)

        if r == sys.stdin:
            f.write('>>> ' + data)
            f.flush()
            p.stdin.write(data)

        if r == p.stdout:
            f.write('<<< ' + data)
            f.flush()
            sys.stdout.write(data)
            sys.stdout.flush()

        if r == p.stderr:
            sys.stderr.write(data)
            sys.stderr.flush()

f.close()