Hi,
at some other forum we had the discussion which is the fastest way to read all files of a directory

• opendir $DIR, $folder; while(my $file = readdir $DIR) ...
• foreach my $file (glob "$folder/*") ...
• opendir $DIR, $folder; my @files = grep { ... } readdir $DIR; foreach my $file (@files) ...

i prefered 1 over 3 because i thought 1 must be faster since 3 will walk all files (at least) twice. so i made a benchmark:

#!/usr/bin/perl

use strict;
use warnings;

use Benchmark qw(:all);

my %folders = (
    Temp1 => 10,
    Temp2 => 100,
    Temp3 => 1000,
    Temp4 => 5000,
    Temp5 => 10000,
    # Temp6 => 20000,
);

foreach my $folder (sort keys %folders) {

    print "Folder: $folder, Files: ", $folders{$folder}, "\n";

    timethese(5, {        
        'Way 1' => sub {
            opendir(my $DIR, $folder) or die "Error: couldn't open dir
+ '$folder': $!\n";
            while(my $file = readdir $DIR) {
                my $filename = "$folder/$file";
                if(-f $filename) {
                # print STDERR "$filename\n";
                }
            }
            closedir($DIR);
        },
        'Way 2' => sub {
            foreach my $file (glob "$folder/*") {
                my $filename = $file;
                if(-f $filename) {
                #   print STDERR "$filename\n";
                }
            }
        },
        'Way 3' => sub {
            opendir(my $DIR, $folder) or die "Error: couldn't open dir
+ '$folder': $!\n";

            my @files = map { "$folder/$_" }
                grep { -f "$folder/$_" }
                readdir($DIR);
            closedir($DIR);

            foreach my $file (@files) {
                my $filename = $file;
              #  print STDERR "$filename\n";
            }
        },
    });
}
[download]

the result does not make sence to me, but maybe you can tell me why

Folder: Temp1, Files: 10
Benchmark: timing 5 iterations of Way 1, Way 2, Way 3...
   Way 1:  0 wallclock secs ( 0.00 usr +  0.00 sys =  0.00 CPU)
           (warning: too few iterations for a reliable count)
   Way 2:  0 wallclock secs ( 0.00 usr +  0.00 sys =  0.00 CPU)
           (warning: too few iterations for a reliable count)
   Way 3:  0 wallclock secs ( 0.00 usr +  0.00 sys =  0.00 CPU)
           (warning: too few iterations for a reliable count)
Folder: Temp2, Files: 100
Benchmark: timing 5 iterations of Way 1, Way 2, Way 3...
   Way 1:  0 wallclock secs ( 0.00 usr +  0.05 sys =  0.05 CPU) @ 108.70/s (n=5)
           (warning: too few iterations for a reliable count)
   Way 2:  0 wallclock secs ( 0.00 usr +  0.08 sys =  0.08 CPU) @ 63.29/s (n=5)
           (warning: too few iterations for a reliable count)
   Way 3:  0 wallclock secs ( 0.03 usr +  0.00 sys =  0.03 CPU) @ 161.29/s (n=5)
           (warning: too few iterations for a reliable count)
Folder: Temp3, Files: 1000
Benchmark: timing 5 iterations of Way 1, Way 2, Way 3...
   Way 1:  1 wallclock secs ( 0.19 usr +  0.63 sys =  0.81 CPU) @  6.15/s (n=5)
   Way 2:  1 wallclock secs ( 0.41 usr +  1.11 sys =  1.52 CPU) @  3.30/s (n=5)
   Way 3:  1 wallclock secs ( 0.16 usr +  0.67 sys =  0.83 CPU) @  6.04/s (n=5)
Folder: Temp4, Files: 5000
Benchmark: timing 5 iterations of Way 1, Way 2, Way 3...
   Way 1:  9 wallclock secs ( 1.20 usr +  7.86 sys =  9.06 CPU) @  0.55/s (n=5)
   Way 2: 19 wallclock secs ( 1.73 usr + 16.59 sys = 18.33 CPU) @  0.27/s (n=5)
   Way 3: 10 wallclock secs ( 0.92 usr +  7.91 sys =  8.83 CPU) @  0.57/s (n=5)
Folder: Temp5, Files: 10000
Benchmark: timing 5 iterations of Way 1, Way 2, Way 3...
   Way 1: 43 wallclock secs ( 3.17 usr + 39.39 sys = 42.56 CPU) @  0.12/s (n=5)
   Way 2: 85 wallclock secs ( 6.53 usr + 76.41 sys = 82.94 CPU) @  0.06/s (n=5)
   Way 3: 42 wallclock secs ( 3.19 usr + 38.06 sys = 41.25 CPU) @  0.12/s (n=5)