Shell magic wanted: format output of hexdump in a pipe

Question

I'm debugging the output of a program that transmits data via TCP. For debugging purposes i've replaced the receiving program with netcat and hexdump:

netcat -l -p 1234 | hexdump -C

That outputs all data as a nice hexdump, almost like I want. Now the data is transmitted in fixed blocks which lengths are not multiples of 16, leading to shifted lines in the output that make spotting differences a bit difficult:

00000000  50 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |P...............|
00000010  00 50 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |.P..............|
00000020  00 00 50 00 00 00 00 00  00 00 00 00 00 00 00 00  |..P.............|

How do I reformat the output so that after 17 bytes a new line is started? It should look something like this:

50 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |P...............|
00                                                |.               |
50 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |P...............|
00                                                |.               |
50 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |P...............|
00                                                |.               |

Using hexdumps -n parameter does not work since it will exit after reaching the number of bytes. (Unless there is a way to keep the netcat programm running and seamlessly piping the next bytes to a new instance of hexdump).

Also it would be great if I could use watch -d on the output to get a highlight of changes between lines.

Answer 1

For hexdump without characters part.

hexdump -e '16/1 "%0.2x " "\n" 1/1 "%0.2x " "\n"'

Answer 2

I use this:

use strict;
use warnings;
use bytes;

my $N = $ARGV[0];

$/ = \$N;

while (<STDIN>) {
    my @bytes = unpack("C*", $_);
    my $clean = $_;
    $clean =~ s/[[:^print:]]/./g;
    print join(' ', map {sprintf("%2x", $_)} @bytes),
    "  |", $clean, "|\n";
}

Run it as perl scriptname.pl N where N is the number of bytes in each chunk you want.

Answer 3

also you can use xxd -p to make a hexdump .