Buffer flush sample

buffer_flush.pl

#!perl
use strict;
use warnings;

use POSIX ();

sysopen my $in, "/proc/net/dev", POSIX::O_RDONLY or die "Can't open file: $!";
open my $out, '>', 'output.log' or die "Can't open file: $!";

#$out->autoflush(1); # <== バッファリングしない(autoflush $out, 1; も可)

my $interval = 3;

while (1) {
    seek $in, 0, POSIX::SEEK_SET; # reset file offset

    printf {$out} "%s", time();

    while (my $buf = <$in>) {
        if ($buf =~ /.+:.+/) {
            chomp $buf;
            $buf =~ s/.+:\s+//;
            printf {$out} "\t%s", $buf;
        }
    }

    printf {$out} "\n";
    $out->flush(); # <== バッファの内容をフラッシュ
    sleep $interval;
}

close $out;
close $in;

buffer_flush.py

#!/usr/bin/env python

import re
import time

input = open("/proc/net/dev")
output = open("log.log", "w")

interval = 3

while True:
    input.seek(0)

    output.write( str(time.time()) )

    for line in input.readlines():
        if re.search(r'.+:.+', line):
            replaced = re.sub(r'.+:\s+', '', line.rstrip('rn'))
            output.write("\t%s" % replaced)

    output.flush()
    output.write("\n")
    time.sleep(3)

close(output)
close(input)