$combined =~ s/[^\x00].*//;

##</code><code>##

¢¼combined=0c0d060a183672756e33 (”Ļ
”č6run3)
$combined=0a183672756e33 (
”č6run3)
Prefix is "model4r"
##</code><code>##

...
$combined =~ s/[^\x00].*//s;
...
##</code><code>##

$combined =~ /^(\x00*)/;
my $prefix = substr($first, 0, length($1));
print qq{Prefix is "$prefix"};