Unfortunately, I can't give more than general help and learning tips. I'm only a casual user of mod_rewrite and don't have an experimental Apache server handy.

On one foot, mod_rewrite lets you use Perl compatible regular expressions to convert a part of a URL you don't like to one you do like. The phrase "Perl compatible" should be taken with a small grain of salt - usually it means some subset of full-blown Perl regexes. I've never really done much more than simple rewrites, so I don't really know how full the emulation is (perhaps some other monk does?).

The hardest part of mod_rewrite is learning its syntax for selecting URLs to be rewritten. In my experience, when mod_rewrite "doesn't work", it is usually a screw up with the selection process: thinking selection criteria are being or'd when they are really being and'd; regexes that don't do what you think they do; accidentally chaining together rules, and so on.

Basically, you define a set of rules for selecting a URL using a series of RewriteCond statements. Each of these has three parts: the word "RewriteCond", a variable representing the thing you want to match (e.g. %{REMOTE_HOST}), and a regex to compare to it. These are the equivalent of $servervar =~ /.../ expressions in Perl.

A series of these RewriteCond statements is normally and'd together but you can "or" them, by adding [OR] at the end of each RewriteCond statement. At the end of all of the RewriteCond statements, is a RewriteRule statement. This contains the URL transformation and has the format:

You can think of it as a fancy version of Perl substitution: s/regex-matching-what-you-want-to-get-rid-of/text-you-actually-want. So your redirection to MolSurfer might look something like this:

RewriteCond %{REMOTE_HOST}  ^host1.*  [OR]
RewriteCond %{REMOTE_HOST}  ^host2.*  [OR]
RewriteCond %{REMOTE_HOST}  ^host3.*
RewriteRule regex replacement-for-regex [R,L]
[download]

The things in square brackets at the end are instructions to the server. [OR] was already discussed above. L means "the end". If it is missing, and there is another set of RewriteCond/RewriteRule statements after it, Apache chains them, just as if you had successive $foo =~ s/blah/blech/ statements in a Perl script. [NC] means ignore case. See the documentation for other codes.

The official documentation is very far from a tutorial, so here are some articles with examples. These should get you started. After reading them, you may want to go back to the mod_rewrite reference page and see if anything there starts making more sense.

• Learn Apache mod_rewrite: 13 Real-world Examples - clearly written intro with examples.
• URL rewriting guide - a little more dense, but lots of examples too.

You might also try searching the net for Apache forums - you are likely to get more detailed help there.

There is also a way you can insert a Perl script to do the URL conversion if you need to get a bit fancier with the conversion or use something like a lookup table stored in a database, but that is a lot more complex than you probabably need right now. If you are interested in it later on, scan the main mod_rewrite documentation page for the word "Perl". They have a short sample script.

Best, beth

Beth,



thank you so much for your time and effort.
After spending some time reading about mod_rewrite, I got the feeling that it is not really what I need. It seems mod_rewrite's intention is to handle complex redirections (and that it becomes really powerful in large networks). Too many bad experiences with "misusing" programs / servers for my needs made me stepping back using it.
After doing more research about http, I realised what I really want is a redirect response back from my cgi.My script above was good, I only needed to change the _location to the requesting one in the http header.

Although I did not use your suggestion, I learned a lot!
Thank you!


#!/usr/bin/perl

use warnings;
use strict;
use Data::Dumper;
use WWW::Mechanize;
use CGI  qw/:standard/;
use CGI::Carp qw(warningsToBrowser fatalsToBrowser);

my $q = new CGI;
my $addr = $ENV{'REMOTE_ADDR'};

my $m = WWW::Mechanize->new();
my $url = 'http://projects.villa-bosch.de/dbase/molsurfer/submit-elec.
+html';


$m->get($url);
$m->add_header(location => $addr);
$m->set_fields(
       FILE1 => $file1,
       FILE2 => $file2,
       mapsize =>'59x59',
       resolution =>'med',
       pdie =>'4',
       sdie =>'80',
       ioss =>'150',
       ionr =>'1.5',
       nmap =>'0.0'
      );  
my $response = $m->submit();
print $q->header;
print $response->content();
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