use Benchmark;
use strict;
my $dir = '/some/small/dir';
my $file = 'somefile*';
opendir (F, $dir);

timethese(5000, {'ls on small dir' => \&foo, 'allready opendir on small dir' => \&bar, 'opening dir on small dir' => \&baz});

$dir = '/some/large/dir';
$file = 'somefile*';
print "\n\n\n";
closedir F;
opendir (F, $dir);
timethese(5000, {'ls on large dir' => \&foo, 'allready opendir on large dir' => \&bar, 'opening dir on large dir' => \&baz});
closedir F;

sub foo
{
    my $a = `ls $dir/$file &>/dev/null`;
}

sub bar
{
    my (@files) = (grep (/$file/, readdir(F)));
    rewinddir (F);
}


sub baz
{
    opendir (DIR, $dir);
    my (@files) = (grep (/$file/, readdir(DIR)));
    closedir F;

}