#!/usr/bin/env perl

use strict;
use warnings;
use autodie;

use Data::Dump;

my @all_order; 

{
    open my $in2_fh, '<', 'pm_1204589_IN2';

    while (<$in2_fh>) {
        chomp;
        push @all_order, $_;
    }
}

for my $range ([0..0], [0..2], [1..3], [3..3]) {
    my %wanted = map { $_ => 1 } @all_order[@$range];

    {
        open my $in1_fh, '<', 'pm_1204589_IN1';

        local $/ = "\n>";

        while (<$in1_fh>) {
            chomp;
            substr $_, 0, 1, '' if $. == 1;
            my ($head, $seq) = split;
            $wanted{$head} = $seq if $wanted{$head};
        }
    }

    print "Range: @$range\n";
    dd \%wanted;
}

##</code><code>##

$ cat pm_1204589_IN1
>Z
ABC
>Y
DEF
>X
GHI
>W
JKL

##</code><code>##

$ cat pm_1204589_IN2
W
X
Y
Z

##</code><code>##

Range: 0
{ W => "JKL" }
Range: 0 1 2
{ W => "JKL", X => "GHI", Y => "DEF" }
Range: 1 2 3
{ X => "GHI", Y => "DEF", Z => "ABC" }
Range: 3
{ Z => "ABC" }