Nothing to add to other monks' comments, but only a few minor advices.

1. You could move the line $dir =~ s/\/$//; just a few lines up and avoid repeating the substitution if more than one .csv file is found in the same $dir. E.g.:

while ( my $dir = shift @ARGV ) {
    my $dh = new DirHandle $dir;
    if ( defined($dh) ) {
        $dir =~ s/\/$//; # Here, for example...
        while ( defined($_ = $dh->read) ) {
            if ( $_ =~ /(\.csv)$/ ) {
                push @files, "$dir/$_";
            }
        }
    }
}
[download]

2. Also, you could slightly simplify your s/// by using another delimiter, for example: s|/$||. It's not a big saving with one slash, but it's worth changing the delimiter when your pattern contains a lot of them

3. When you manipulate $_ you could want to localize it, to avoid clashes with functions or modules that use it (like File::Find, for example). It's not the case of your simple program, of course.

4. (but I guess you already know :-) if you want, you can leave out the $_ =~ from your pattern match.

Just my 0.02 EUR

Ciao!
--bronto

# Another Perl edition of a song:
# The End, by The Beatles
END {
  $you->take($love) eq $you->made($love) ;
}