You could use regular expressions, perldoc perlre:

use warnings;
use strict;

my $search;
my $cmdout = "some words\nHello i like Perlmonks.org \n more words";
if ($cmdout =~ / \n ( .* Perlmonks\.org .*) \n /sx) {
    $search = $1;
    print "$search\n";
}

__END__
Hello i like Perlmonks.org
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