Use a hash of arrays 
my %matches;
my $section;
...
if ( $line =~ m/^(Router|Network|Extern)/ ) {
  $section = $1;
}
push @{ $matches{$section} }, $line;

[download]

And I'd stay clear of Switch if I were you. It can lead to some difficult to trace bugs.

update

Here's a reimplementation of your subroutine, along with example usage

use Data::Dumper;

my $matches = ospf2_split_database(
    "no match\n",
    "Extern 1\n",
    "Network 1\n",
    "Stuff for Network 1a\n",
    "Stuff for Network 1b\n",
    "Stuff for Network 1c\n",
    "Network 2\n",
    "Stuff for Network 2a\n",
    "Stuff for Network 2b\n",
    "Router 1\n",
    "Router 2\n",
    "Extern 2\n",
);

print Dumper $matches->{Network};

sub ospf2_split_database {
    my %matches;
    my @ospf2database = @_;

    my $section;
    for my $line ( @ospf2database ) {
        chomp $line;
        if ( $line =~ m/^(Router|Network|Extern)/ ) {
            $section = $1
        }
        push @{ $matches{$section} }, $line
          if $section;
    }
    return \%matches;
}

[download]

Update^2: Now meets the clarified spec

In reply to Re: Is there a better way to approach this? by FunkyMonk
in thread Is there a better way to approach this? by ewhitt

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