To count the number of files in mydir you could use:

#!/usr/bin/perl
use strict;
use warnings;

my $dirname = "/mydir";

opendir ( DIR, $dirname ) || die "Error in opening dir $dirname\n";
my $count;
while ( (my $filename = readdir(DIR)) ) {
  next if $filename =~ /^\.{1,2}$/; # skip . and ..
  $count++;
}
closedir(DIR);

print "$count files live in '$dirname'\n";
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