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

use Path::Tiny;


setup();
# This is the solution:
for my $file (path('test1')->children) {
    $file->copy('test2') unless path('test2/' . $file->basename)->exists;
}


sub setup {
    my %structure = (
                     test1 => [qw( abc.txt xyz.txt         )],
                     test2 => [qw( abc.txt sdf.txt fgh.txt )],
                    );

    my $i = 0;
    for my $dir (keys %structure) {
        for my $file (@{ $structure{$dir} }) {
            path("$dir/$file")->touchpath->spew($i++);
        }
    }
}