$cgi->script_name() or $ENV{SCRIPT_NAME} for the url of the script relative to the root url of the server.

Until you do a chdir, rel2abs($0) gives the absolute file system path to the script.

My server provides the document root in $ENV{DOCUMENT_ROOT}.

Combined with File::Spec and CGI, you have all you need.

Update: Example:

use File::Basename        qw( dirname );
use File::Spec::Functions qw( rel2abs );

my $script_path = rel2abs($0);
my $script_dir  = dirname($script_path);
my $script_url  = $ENV{SCRIPT_NAME};
my $doc_root    = $ENV{DOCUMENT_ROOT};

my $redirect_to = URI->new_abs('bar.cgi', $script_url); # /dir/bar.cgi
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I can't come up with any reason to use $script_path or $doc_root.

Hello - and thank you for the hints. Unfortunately script_name or getcwd return the location of the script in the filesystem (let's say c:\test\test.pl). This can be mapped in to various addresses using the Virtual Folder option of IIS. If my site is at d:\webroot and test is aliased as http://localhost/somename, I can find my location as c:\test\test.pl or /somename/test.pl but have no hints on the existence of d:\webroot

Like I already said, my server provides the document root in $ENV{DOCUMENT_ROOT}. Check your server's documentation or just dump the environment variables

#!/usr/bin/perl
use strict;
use warnings;
use List::Util qw( max );
print("Content-Type: text/plain\n\n");
my $max_size = max map length, keys %ENV;
my $format = "%-" . ($max_size+1) . "s %s\n";
for (sort keys %ENV) {
   printf($format, "$_:", $ENV{$_});
}
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Then IIS is broken. For url
http://server.port/this/is/all/SCRIPT_NAME?que=ry
SCRIPT_NAME =/this/is/all/SCRIPT_NAME

The documentation ( IIS Server Variables ) confirms this.