Here's a variation that doesn't require an unusual trailing backslash, gives a better error message, and avoids using global variables:

use File::Spec::Functions qw( catfile );

my $dir = "e:\\core\\ops_utilities";
opendir(my $dh, $dir)
   or die("Unable to read utilities directory \"$dir\": $!\n");

my @files = grep { !-d catfile($dir, $_) } readdir($dh);
[download]

The following might be more useful:

my @files = grep { !-d }
            map { catdir($dir, $_) }
            readdir($dh);
[download]