Question

Are both of the examples below OK, or is the second one bad style?

Case 1: Stay in top directory and use catdir to access subdirectories

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

my $dir = 'my_dir_with_subdir';
my ( $count, $dh );

use File::Spec::Functions;
$count = 0;

opendir $dh, $dir or die $!;
while ( defined( my $file = readdir $dh ) ) {
    next if $file =~ /^\.{1,2}$/;
    my $sub_dir = catdir $dir, $file;
    if ( -d $sub_dir ) {
        opendir my $dh, $sub_dir or die $!;
        while ( defined( my $file = readdir $dh ) ) {
            next if $file =~ /^\.{1,2}$/;
            $count++;
        }
        closedir $dh or die $!;
    }
    else {
        $count++;
    }
}

closedir $dh or die $!;
print "$count\n";

Case 2: Change to subdirectories and restore top directory before exit

use Cwd;
my $old = cwd;
$count = 0;
opendir $dh, $dir or die $!;
chdir $dir or die $!;
while ( defined( my $file = readdir $dh ) ) {
    next if $file =~ /^\.{1,2}$/;
    if ( -d $file ) {
        opendir my $dh, $file or die $!;
        chdir $file or die $!;
        while ( defined( my $file = readdir $dh ) ) {
            next if $file =~ /^\.{1,2}$/;
            $count++;
        }
        closedir $dh or die $!;
        chdir $dir;
    }
    else {
        $count++;
    }
}
closedir $dh or die $!;
chdir $old or die $!;
print "$count\n";

Answer 1

For your example, it’s best to change to subdirectories, and don’t bother changing back to the original directory at the end. That’s because each process has its own “current directory”, so the fact that your perl script is changing it’s own current directory does not mean that the shell’s current directory is changed; that stays unaltered.

If this was part of a larger script it would be different; my general preference then would be not to change directory, just to reduce confusion over what the current directory is at any point in the script.