#!/usr/bin/perl

use strict;
use warnings;

my %switches = (switch0 => [qw/switch1 switch2 switch3/],
                switch1 => [qw/switch4/],);
                
my $start    = 'switch0';

print_tree(\%switches,$start,0);

sub print_tree{
    my ($hashref,$start,$level) = @_;
    
    my $whitespaces = ' ' x ($level * 5);
    print $whitespaces.$start,"\n";
    
    for my $switch(@{$hashref->{$start}}){
        if(exists $hashref->{$switch}){
            print_tree($hashref,$switch,$level+1);
        }
        else{
            my $whitespaces = ' ' x (($level+1) * 5);
            print $whitespaces.$switch,"\n";            
        }
    }
}