#!/usr/bin/perl -w
#
# Proof-of-concept for using minimal memory to search huge
# files, using a sliding window, matching within the window,
# and using on /gc and pos() to restart the search at the
# correct spot whenever we slide the window.
#
# Doesn't correctly handle potential matches that overlap;
# the first fragment that matches wins.
#

use strict;
use constant BLOCKSIZE => (8 * 1024);

&search("bighuge.log",
        sub { print $_[0], "\n" },
        "<img[^>]*>");

sub search {
    my ($file, $callback, @fragments) = @_;

    local *F;
    open(F, "<", $file) or die "$file: $!";
    binmode(F);

    # prime the window with two blocks (if possible)
    my $nbytes = read(F, my $window, 2 * BLOCKSIZE);

    my $re = "(" . join("|", @fragments) . ")";

    while ( $nbytes > 0 ) {

        # match as many times as we can within the
        # window, remembering the position of the
        # final match (if any).
        while ( $window =~ m/$re/oigcs ) {
            &$callback($1);
        }
        my $pos = pos($window);

        # grab the next block
        $nbytes = read(F, my $block, BLOCKSIZE);
        last if $nbytes == 0;

        # slide the window by discarding the initial
        # block and appending the next. then reset
        # the starting position for matching.
        substr($window, 0, BLOCKSIZE) = '';
        $window .= $block;
        $pos -= BLOCKSIZE;
        pos($window) = $pos > 0 ? $pos : 0;
    }

    close(F);
}

##</code><code>##

while ( $window =~ m/$re/oigcs ) {
            &$callback($1);
        }


##</code><code>##

while ( $window =~ m/\w{3}\s{1,2}\d{1,2}.*$re.*\n/oigc ) {
            &$callback($1);
        }


##</code><code>##

Feb 24 04:03:47 server sendmail[]: khdkahsdad876sad8: to=<sample@collegeclub.com>, delay=1+13:12:11, xdelay=00:00:00, mail
er=esmtp, pri=25672345, relay=collegeclub.com., dsn=4.0.0, stat=Deferred: Connection timed out with collegeclub.com.
Feb 24 04:03:47 server sendmail[31356]: madhksadkh5574: to=<sample@iit.edu>, delay=1+13:20:32, xdelay=00:00:00, mailer=esmtp,
 pri=26574dffd, relay=sample.iit.edu. [006.47.143.000], dsn=4.3.1, stat=Deferred: 452 sample 4.2.1 Mailbox temporarily disabled: sample@iit.edu