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

use List::Util 'reduce';
use Path::Tiny 'path';

my @files = qw/a b c/;
my $dir = '/tmp/';

print newest($dir, @files) . "\n";

sub newest {
    my $dir = shift;
    my $newest = reduce { $a->stat->mtime > $b->stat->mtime ? $a : $b }
        map { path "$dir/$_" }
        @_;
    return "$newest";
}