See updated code below. 

#!/usr/bin/perl
use CGI;
my $q = new CGI;

print
  $q -> header,
  $q -> start_html( -base => { 'href' => '$url' }),
  $q -> p( 'blah, blah' ),
  $q -> end_html;

[download]

output: 

<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE html
    PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
      lang="en-US" 
      xml:lang="en-US">
      
<head>
<title>Untitled Document</title>
<base href="http://localhost/answer.pl" />
</head>

<body>
<p>blah, blah</p>
</body>

</html>

[download]

Updated

Added output

Update 2

I should have used strict and warnings to catch the undeclared $url (and not put it in quotes).

Also the docs says:

The argument -xbase allows you to provide an HREF for the <base> tag different from the current location

#!/usr/bin/perl

use strict;
use warnings;

use CGI;
my $q = new CGI;
my $url = 'docroot/';

print
  $q -> header,
  $q -> start_html( 
    -title => 'Adding base to header',
    -base  => 'true',
    -xbase => $url,
  ),
  $q -> p('blah, blah'),
  $q -> end_html;

[download]

In reply to Re: Base urls using Perl CGI by wfsp
in thread Base urls using Perl CGI by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.