use warnings;
use strict;

my $word_a = next_from_array();
my $word_f = next_from_file();

while ( 1 ) {
  last unless defined $word_f and defined $word_a;
  if ( $word_f lt $word_a ) {
    $word_f = next_from_file();
  }
  elsif ( $word_a lt $word_f ) {
    $word_a = next_from_array();
  }
  else {
    process( current_line() );
#    $word_a = next_from_array();
    $word_f = next_from_file();
  }
}

{
  INIT { reset_array(); }
  {
    my ( $i, @array );
    sub reset_array {
      @array = qw( item1 item2 item4 item5 );
      $i = 0;
    }

    sub next_from_array {
      return $i < @array ? $array[ $i++ ] : ( $i = 0, undef );
    }
  }

  INIT {
    my $filename = shift || die "Usage: blah blah blah\n";
    reset_file( $filename );
  }

  {
    my ( $in, $line );
    sub reset_file {
      my $filename = shift;
      use PerlIO::gzip;
      my $mode = '<:gzip';
      open $in, $mode, $filename or die "can't read $filename: $!\n";
    }

    sub next_from_file {
      local $_ = $line = <$in> and chomp;
      return defined $_ ? ( split /\t/ )[ -1 ]
        : ( reset_file(), undef );
    }

    sub current_line {
      return $line;
    }
  }
}

sub process {
  local $| = 1;
  print shift;
}
__END__