You can do this using either BFS or DFS. Recursive method call is a great way to solve this kind of problems.

#!/usr/bin/perl -w

use strict;

sub bfs
{
    my $dir = shift;

    return unless defined $dir;

    opendir(my $dh, $dir) || die;
    while (readdir $dh) {
        next if /^\.{1,2}$/;
        $_ = "$dir/$_";
        if (-d) {
            push @_, $_; ###
        } elsif (-f) {
            print "$_\n";
        } else {
            print "Something else: $_\n";
        }
    }
    closedir $dh;

    bfs(@_);
}

sub dfs
{
    my $dir = shift;

    return unless defined $dir;

    opendir(my $dh, $dir) || die;
    while (readdir $dh) {
        next if /^\.{1,2}$/;
        $_ = "$dir/$_";
        if (-d) {
            unshift @_, $_; ###
        } elsif (-f) {
            print "$_\n";
        } else {
            print "Something else: $_\n";
        }
    }
    closedir $dh;

    dfs(@_);
}

print "=== BFS ===\n";
bfs(@ARGV);

print "=== DFS ===\n";
dfs(@ARGV);
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