Как можно ограничить размер сохраняемого вывода?

#!/bin/sh
out=1
i=1
while read line; do
  if [ $i -gt 1000 ]; then
    # switch outfile
    if [ $out == '1' ]; then
       out=2
    else
       out=1
    fi

    # truncate new file
    :>/tmp/xsession${out}.log

    # drop line's counter
    i=1
  fi
  echo "$line" >> /tmp/xsession${out}.log
  i=$(($i+1))
done

#!/usr/bin/env python2

import sys, fcntl, os
from select import select

def swap(names, idx):
    return open(names[idx], 'wb', 0), (idx + 1) % len(names)

def main(size, filename):
    infile = sys.stdin.fileno()
    fl = fcntl.fcntl(infile, fcntl.F_GETFL)
    fcntl.fcntl(infile, fcntl.F_SETFL, fl | os.O_NONBLOCK)

    names = [filename + '.0', filename + '.1']
    outfile, idx = swap(names, 0)
    collected = 0
    while True:
        readable, _, _ = select([infile], [], [])
        if readable:
            f = readable[0]
            while True:
                try:
                    data = os.read(f, 1024)
                except OSError, e:
                    if e.errno == 11:
                        data = None
                    else:
                        raise

                if not data:
                    break

                collected += os.write(outfile.fileno(), data)
                if collected > size:
                    outfile.close()
                    outfile, idx = swap(names, idx)
                    collected = 0

if __name__ == '__main__':
    main(int(sys.argv[1]), sys.argv[2])