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

my @output;
use constant { STATE_IDLE=>0, STATE_IN_SECTION=>1 };
my $state = STATE_IDLE;
my @buf;
my $end_section = sub {
	if ( $state == STATE_IN_SECTION )
		{ push @output, [@buf]; @buf = () }
	$state = STATE_IDLE;
};
while (<DATA>) {
	chomp;
	if ( my ($x,$y) = /^ (?: (.+) \s+ )? START (?: \s+ (.+) )? $/x ) {
		if ( defined $x ) {
			die "unexpected: $_\n" unless $state == STATE_IN_SECTION;
			push @buf, $x;
		}
		$end_section->();
		$state = STATE_IN_SECTION;
		push @buf, $y if defined $y;
	}
	elsif ( my ($z) = /^ (?: (.+) \s+ )? END $/x ) {
		die "unexpected: $_\n" unless $state == STATE_IN_SECTION;
		push @buf, $z if defined $z;
		$end_section->();
	}
	else {
		if ( $state == STATE_IN_SECTION )
			{ push @buf, $_ }
		else {} # ignore outside of section
	}
}
$end_section->();

use Test::More tests=>1;
is_deeply \@output, [["a", "b"], ["c" .. "g"], ["h", "i"], ["j", "k"]]
	or diag explain \@output;

__DATA__
START
a
b
START c
d
e
f
g END
ignoreme
START h
i START j
k