Write both hex and char representation side by side.

Replace non-printing chars by ".".
use strict;
use locale;

in short: Almost completely new :-)

tcpdump_tools/tcpdump2ascii

@@ -1,15 +1,22 @@
-#!/usr/bin/perl
+#!/usr/bin/perl -w
+use strict;
+use POSIX;
+use locale;
+
+$| = 1;
 
 while(<>) {
 	if (/^\t\t\t( [0-9a-f]{2,4})+$/) {
-		@hex = split;
-		foreach $i (@hex) {
-			@c = pack("H4", $i);
-			foreach $j (@c) {
-				print "$j";
+		chomp;
+		my @hex = split;
+		my $line = "$_  ";
+		foreach my $i (@hex) {
+			my @c = pack("H4", $i);
+			foreach my $j (split(//, "@c")) {
+				$line .= isprint($j) ? "$j" : ".";
 			}
 		}
-		print "\n";
+		print "$line\n";
 	} else {
 		print
 	}