I'm all for TIMTOWTDI, but I wondered about performance. And it turns out that while a split version is faster for short strings, performance suffers a lot the more commas there are in the string:

use warnings;
use strict;
use Benchmark qw/cmpthese/;

my $str = join ',', 'a'..'z', 5;
my $exp_path = join ',', 'a'..'z';
my $exp_value = 5;

cmpthese(-2, {
    split => sub {
        my @x = split /,/, $str;
        my ($path, $value);
        $value = pop @x if @x>1;
        $path = join ',', @x;
        #die unless $path eq $exp_path && $value eq $exp_value;
    },
    regex => sub {
        my ($path, $value) =
            $str=~/^ (?| ([^,]*) | (.*) , ([^,]*) ) $/x;
        #die unless $path eq $exp_path && $value eq $exp_value;
    },
} );

__END__

          Rate split regex
split 326127/s    --  -66%
regex 966896/s  196%    --
[download]

Update: This version using rindex beats both split and the regex.