$ perl chdir_benchmar
Benchmark: timing 1000 iterations of with_chdir, without_chdir...
with_chdir: 16 wallclock secs ( 8.11 usr +  8.46 sys = 16.57 CPU)
  @ 60.35/s (n=1000)
without_chdir: 31 wallclock secs (10.98 usr + 19.15 sys = 30.13 CPU)
  @ 33.19/s (n=1000)

##</code><code>##

#!/usr/bin/perl

use warnings;
use strict;
use Benchmark;

sub with_chdir
{
  my $d = shift;
  my $filecount = 0;
  chdir($d) or die "chdir: $!\n";
  opendir(DIR,".");
  while(my $f = readdir(DIR))
  {
    ( -f $f) and $filecount++;
  }
}

sub without_chdir
{
  my $d = shift;
  my $filecount = 0;
  opendir(DIR,$d);
  while(my $f = readdir(DIR))
  {
    ( -f "$d/$f") and $filecount++;
  }
}

use constant TESTDIR => "/var/mail";

timethese(100, {
                 with_chdir => sub { with_chdir(TESTDIR); },
                 without_chdir => sub { without_chdir(TESTDIR); },
                });