My thoughts were to just make MyCapture a subclass of Tie::Handle::Scalar that registers callbacks. Here's an example MyCapture.pm that is similar to your STDOUT::Capture module. You could go ahead and provide a wrapper module that hardcodes the desired callbacks as you do, or hardcode them directly in this subclass.

## -- MyCapture.pm -- ##
package MyCapture;
use Tie::Handle::Scalar;
our @ISA = qw/Tie::Handle::Scalar/;
my %callbacks;

sub import {
  my $self = shift;
  %callbacks = @_;
}

sub PRINT {
  my $self = shift;
  my $input = join '', @_;
  if(exists $callbacks{on_print}){
    $callbacks{on_print}->(\$input);
  }
  $self->SUPER::PRINT($input);
}

sub DESTROY {
  my $self = shift;
  if(exists $callbacks{on_finish}){
    $callbacks{on_finish}->($self->{data});
  }
  print ${$self->{data}};
}

1;
__END__

## -- test.pl -- ##
#!/usr/bin/perl -w
use strict;
use CGI qw(:standard);
use MyCapture on_finish => \&on_finish,
              on_print  => sub{${$_[0]} =~ s/\bcgi\b/CGI/g};

sub on_finish {
  my $input = shift;
  $$input =~
    s{(</head>)}
    {<link rel="stylesheet" type="text/css" href="/css/style.css" />\n
+$1}i;
}

tie *STDOUT, 'MyCapture';

print header;
print start_html(-title => 'Cool cgi program');
print h1('Welcome to my cool cgi!');
print p('This is just a test page.');
print end_html;

untie *STDOUT;

__END__

[download]

In reply to Re: Re(2): STDOUT::Capture - manipulate STDOUT by Anonymous Monk
in thread STDOUT::Capture - manipulate STDOUT by Dog and Pony

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.