use strict;
use warnings;

my $data = "line1\nfoobar\nline3\n";

$data =~ s{(foo)(bar)}{ my $one = $1; my $two = $2; $one .= <<'END_TEXT'; $one.$two; }e;

Insert 1
Insert 2
END_TEXT


print $data;

##</code><code>##

Microsoft Windows XP [Version 5.1.2600]
(C) Copyright 1985-2001 Microsoft Corp.

C:\Documents and Settings\Neva>cd \code\Jff

C:\code\JFF>perl regex.pl
line1
foo
Insert 1
Insert 2
bar
line3