The problem is that (in *ix) the long path "/var/log/../../home/poletti/../../etc/passwd" does not necessarily compact to "/etc/passwd". For example, if "/home/poletti" was a symbolic link to "/drive2/home/poletti", the long path would compact to "/drive2/etc/passwd". That's why canonpath does not eliminate "segment/../" in *ix.

Update: Here's some code that does the trick, ignoring symbolic links:

use File::Spec::Unix ();

sub remove_dot_dot {
   local $_ = $_[0];
   $_ = File::Spec::Unix->canonpath($_);
   1 while s#[^/]+/\.\./##g;
   s#/[^/]+/\.\.$#/#g;
   s#^[^/]+/\.\.$#.#g;
   return $_;
}
[download]

Tests:

printf("%-20s -> %-20s\n", $_, remove_dot_dot($_))
   foreach (qw(
      /foo/..
      /foo/../bar
      foo/..
      foo/../bar
      ..
      ../foo
      ../foo/bar
      foo/bar/../..
      /foo/bar/../..
      /foo/bar/../../moo
      /var/log/../../home/poletti/../../etc/passwd
   ));

__END__
output
======
/foo/..              -> /
/foo/../bar          -> /bar
foo/..               -> .
foo/../bar           -> bar
..                   -> ..
../foo               -> ../foo
../foo/bar           -> ../foo/bar
foo/bar/../..        -> .
/foo/bar/../..       -> /
/foo/bar/../../moo   -> /moo
/var/log/../../home/poletti/../../etc/passwd -> /etc/passwd
[download]

Update2: I got confused and thought ../foo/bar should give bar. Fixed.