use warnings;

$template = 'D<';
$nv = 2.4;
$p = pack $template, $nv;

$s = "'$p'";

# Now pass $p to the 'double' build of perl.
$double_perl = "C:/perl-5.34.0/bin/MSWin32-x64-multi-thread/perl.exe";
system $double_perl, '-wle', "print unpack('H*', $s);";