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


my $f = "31FCFFFFFFFFFFFE5817300618262527262123216E5D5346172D620000C00000000000000000262F2D2D2D2E2D00008000000150591200A832C001D026252222893360808026187CFF";
$f = pack("H*",$f);

# substr EXPR,OFFSET,LENGTH,REPLACEMENT

print "Number of bytes: ", length $f, "\n";
printf "record Len? : %x  hex \n",ord(substr($f,0,1));
print  "record Len? : ", ord(substr($f,0,1))," decimal \n";
print  "not right first byte, ASCII '1':", substr($f,0,1),"\n"; ##ASCII "1";

__END__
Prints:
Number of bytes: 73
record Len? : 31  hex 
record Len? : 49 decimal 
not right first byte, ASCII '1':1