The following should check for files which only exist in dir1 and copy them to dir2 (UNTESTED):

use strict; 
use warnings; 
use File::Slurp qw(read_dir);
use File::Copy;

my $dir1 = 'C:\TEST1';
my $dir2 = 'C:\TEST2';

my %files1 = map { $_ => 1 } grep { -f "$dir1/$_" } read_dir($dir1);

opendir my $dh, $dir2 or die "can not open $dir2: $!";
while (my $entry = readdir $dh) {
    next unless -f "$dir2/$entry";
    copy("$dir1/$entry" => "$dir2/$entry") unless exists $files1{$entr
+y};
}
closedir $dh;
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