This sooo looks like homework. Oh, well.

You'll probably be interested in the s modifier for regex matching. (See perlre for more detail.):

#!/usr/bin/perl
use strict;
use warnings;

my $poem;

{
        local $/ = undef;
        $poem = <DATA>;
}

my( $before, $after) = $poem =~ m/(.*)\bDOG\b(.*)/s;

print "Text before:\n$before\n\n";
print "Text after:\n$after\n\n";

__DATA__
A Beautiful Poem
Mary had a little lamb, little lamb, little lamb
Mary had a DOG but everywhere that mary went the lamb was
sure to go even though it did not like the dog very much.


# Output

Text before:
A Beautiful Poem
Mary had a little lamb, little lamb, little lamb
Mary had a

Text after:
 but everywhere that mary went the lamb was
sure to go even though it did not like the dog very much.
[download]

---

---

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! —

• How do I compose an effective node title?
• How do I post a question effectively?
• Markup in the Monastery

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:
	&		&
	<		&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.