$_ = my $original = "/one/two///three/four/..//fourX/five////six/seven";

# you can do job 1 alone like this:

tr!/!/!s;
print "1: $original -> $_\n";

# OR you can do jobs 1 and 2 together like this;

my @srcpaths = split m!/+!, $original;
my @outpaths = ();
for my $p ( @srcpaths ) {
    if ( $p eq '..' ) {
        pop @outpaths;
    } else {
        push @outpaths, $p;
    }
}
$_ = join( "/", @outpaths );

print "2: $original -> $_\n";