#!/usr/bin/perl

$dir = shift || '.';

my $latest = (sort {$b->{mtime} <=> $a->{mtime}}
             map {{mtime => -M $_, file => $_}}
             <$dir/*>)[-1];

print $latest->{file}, "\n";

#Using map allows -M to be performed on each file only once  
#per sort iteration. 
#once will save a lot of CPU time.