#!/usr/bin/perl

use strict;
use warnings;
use feature qw[signatures say state];
no warnings 'experimental::signatures';

say readN('input.txt', 4) for 1 .. 3;

sub readN ($filename, $n) {
  state %fh;

  unless ($fh{$filename}) {
    open $fh{$filename}, '<', $filename
      or die "Cannot open '$filename': $!\n";
  }

  read $fh{$filename}, my ($buf), $n;

  return $buf;
}