I had to deal with a similar situation one time. Instead of fiddling with a regex all day, I used split to split the path up, and then put it back together (minus the last part). It was similar to this:

my $oldpath = "/foo/bar/baz";
my @path = split(/\//, $oldpath);
my $newpath = "";
for ($i=0; $i<(@path-1); $i++)
{
     $newpath .= "/".$path[$i]; 
}
print $newpath;
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It might not be as cleany coded as a regex (or as cool looking!), but it gets the job done. Sometimes the simple solutions are the best :)