Hello my friends,

I'd like to extract a png-file out of a huge file like a memory dump. In this example the png-file sits an the very beginning, so I just have to search for the end-string ("IEND"-string).

My idea is to read the file char-by-char, then read 4 bytes ahead and check these 4 bytes for the matching "IEND"-string, then put the pointer back to the old position and write the char into the new file.

Unfortunately it works only when the matching string is located not far from the beginning of the file. My test-png sizes 5.5kb and the code exits after 193 bytes in the middle of nowhere.

What am I doing wrong?

#!/usr/bin/env perl
use strict;
use warnings;

my $dateiread = "/home/ni/OUTPUT/test.png";
my $dateiwrite = "/home/ni/OUTPUT/test2.png";
my $buffer;
my $zeichen;
my $bytes = 4;

open (my $handle1, "<", $dateiread); 
open (my $handle2, ">", $dateiwrite); 

while (my $zeichen = getc($handle1))
    {
    seek($handle1, -1, 1);
    read($handle1, $buffer, $bytes);
    if ($buffer =~ /IEND/g)
        {
        print $handle2 $buffer;
        exit;
        }
    seek($handle1, -3, 1);
    print $handle2 $zeichen;
    }
close ($handle1);
close ($handle2);

[download]

Another question:
is my method suitable for handling large dumpfiles (2gb for example) or is there a faster one?

Sincerely,
Ni

In reply to File extraction 2nd try by knight.of.ni

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