Why does this relative file path work?

On a shared Linux/Apache host, my directory structure is as follows:

home
data
HTML
cgi
topic
downloads

topic contains page.html (and also the "downloads" directory). page.html
contains a link to cgi/script.pl. script.pl increments a count in a data
file and then redirects the client to download a file:

$k_counts_filepath = "../../data/hes_dl_counts.txt";
$k_target_dir_uri = "../../topic/downloads/";
# code to validate existence of download target and to increment counter
goes here
if ($ok) {
print "Location: $k_target_dir_uri$targetname\n";
print "Status: 302 Found\n\n"; }
else {
print "Status: 404 Not found\n\n"; }

The double-up (../..) in the path to the file in the "data" directory seems
straightforward; it's relative to the cgi directory which contains the
script.

But notice the ../.. in the path to the "downloads" directory. Wanting to
use a relative rather than absolute path I arrived at this by trial and
error, but I don't understand why it works. What is the base directory that
the "../.." is being applied to?

--
For mail, please use my surname where indicated:
steve@surname.reno.nv.us (Steve Brecher)

On Fri, 4 Jul 2003, Steve Brecher <see@my.signature.at.end> wrote:
> On a shared Linux/Apache host, my directory structure is as follows:
>
> home
> data
> HTML
> cgi
> topic
> downloads
>
> topic contains page.html (and also the "downloads" directory). page.html
> contains a link to cgi/script.pl. script.pl increments a count in a data
> file and then redirects the client to download a file:
>
> $k_counts_filepath = "../../data/hes_dl_counts.txt";
> $k_target_dir_uri = "../../topic/downloads/";
> # code to validate existence of download target and to increment counter
> goes here
> if ($ok) {
> print "Location: $k_target_dir_uri$targetname\n";
> print "Status: 302 Found\n\n"; }
> else {
> print "Status: 404 Not found\n\n"; }
>
> The double-up (../..) in the path to the file in the "data" directory seems
> straightforward; it's relative to the cgi directory which contains the
> script.
>
> But notice the ../.. in the path to the "downloads" directory. Wanting to
> use a relative rather than absolute path I arrived at this by trial and
> error, but I don't understand why it works. What is the base directory that
> the "../.." is being applied to?

You do not need a Status: header for a redirect (apache does that
automatically for Location:).

You have one too many "../" in there. If this was a /~user/ URL it would
not work. But apparently you have a virtual host and a URI path cannot go
above the root of your website, so from cgi dir, the following should all
end up in the same place:

/topic/downloads/ (full URI path)
.../topic/downloads/ (relative path, did this not work?)
.../../topic/downloads/ (backtracking above URI root ignored)

I don't know whether apache or the browser generated the proper path for
the redirect. But the browser needs to construct a full URL path for an
HTTP request and it cannot go above URI root.

If something did not work with the actual relative path, either you made a
typo or there is something unusual about your server config that we cannot
see here.

--
David Efflandt - All spam ignored http://www.de-srv.com/
http://www.autox.chicago.il.us/ http://www.berniesfloral.net/
http://cgi-help.virtualave.net/ http://hammer.prohosting.com/~cgi-wiz/

"David Efflandt" <efflandt@xnet.com> wrote:
> On Fri, 4 Jul 2003, Steve Brecher <see@my.signature.at.end> wrote:
> > On a shared Linux/Apache host, my directory structure is as follows:
> >
> > home
> > data
> > HTML
> > cgi
> > topic
> > downloads
> >
> > topic contains page.html (and also the "downloads" directory).
page.html
> > contains a link to cgi/script.pl. script.pl increments a count in a
data
> > file and then redirects the client to download a file:
> >
> > $k_counts_filepath = "../../data/hes_dl_counts.txt";
> > $k_target_dir_uri = "../../topic/downloads/";
> > # code to validate existence of download target and to increment counter
> > goes here
> > if ($ok) {
> > print "Location: $k_target_dir_uri$targetname\n";
> > print "Status: 302 Found\n\n"; }
> > else {
> > print "Status: 404 Not found\n\n"; }
> >
> > The double-up (../..) in the path to the file in the "data" directory
seems
> > straightforward; it's relative to the cgi directory which contains the
> > script.
> >
> > But notice the ../.. in the path to the "downloads" directory. Wanting
to
> > use a relative rather than absolute path I arrived at this by trial and
> > error, but I don't understand why it works. What is the base directory
that
> > the "../.." is being applied to?
>
> You do not need a Status: header for a redirect (apache does that
> automatically for Location:).

Noted.

> You have one too many "../" in there. If this was a /~user/ URL it would
> not work. But apparently you have a virtual host and a URI path cannot go
> above the root of your website, so from cgi dir, the following should all
> end up in the same place:
>
> /topic/downloads/ (full URI path)
> ../topic/downloads/ (relative path, did this not work?)

(This is now irrelevant because I am persuaded that what is needed to comply
with CGI best practice is either an entire URL or a complete path; however,
for the record...)

It didn't work; the server reported that the URL
/~myaccount/cgi/topic/downloads/target.file
was not found on the server.

> ../../topic/downloads/ (backtracking above URI root ignored)

As noted originally, this worked.

--
For mail, please use my surname where indicated:
steve@surname.reno.nv.us (Steve Brecher)