#!/usr/bin/perl

#author : morphad
#date   : 2013-12-26

use warnings;
use strict;

use IO::File;
use Fcntl;

sub hexdump
{
    my $data = shift;
    my $offset = shift;
    my @darray = unpack("C*",$data);
    my $idx = $offset - $offset % 16;
    if ($idx != $offset)
    {
        printf "%08X | ",$idx;
        while ($idx < $offset)
        {
            printf " " if (($idx % 2) == 0);
            printf "--";
            $idx++;
        }
    }

    $idx = $offset;
    foreach my $byte (@darray)
    {
        if (($idx % 16) == 0)
        {
            printf "\n" if ($idx != 0);
            printf "%08X | ",$idx;
        }
        printf " " if (($idx % 2) == 0);
        printf "%02X",$byte;
        $idx++;
    }
    printf "\n\n";
}

sub usage
{
    print "usage : hexdump.pl file offset len\n";
    print "hexdump content of file,len bytes at offset\n";
    exit 2;
}

my $file = shift;
my $offset = shift;
my $len = shift;

unless ($file && $offset && $len)
{
    usage;
}

my $fh = IO::File->new();
$fh->binmode(":raw");

unless ($fh->open($file,"<")) {
    die "cannot open $file";
}

my $buf;
my $readn;

$fh->seek($offset,SEEK_SET);
$readn = $fh->read($buf,$len) || die "cannot read buf";
die "read err" if ($readn != $len);

print "=====hex dump [$file]\n";
hexdump $buf,$offset;

$fh->close();

1;