#!/usr/bin/env perl

use strict;
use warnings;
use autodie;

my $name_file = 'names.txt';

open my $name_file_fh, '<', $name_file;
chomp(my @names = <$name_file_fh>);
close $name_file_fh;

print 'Enter login name: ';
chomp(my $input = <STDIN>);

print "Invalid!\n" unless grep { $_ eq $input } @names;