为何CMD运行如下Perl代码不能进行copy？

#!/usr/bin/perl
use strict;
use warnings;my $newDir="files";
unless(-d $newDir)
{
mkdir $newDir or die $!;
}my @allFiles=glob("*");
foreach my $subDir(@allFiles)
{
if(-d $subDir)
{
opendir(SUB,".\\$subDir") or die $!;
while(my $file=readdir(SUB))
{
if($file=~/\.gz$/)
{
`copy .\\$subDir\\$file .\\$newDir`;
}
}
close(SUB);
}
}