#!/usr/bin/perl -w
use Data::Dumper;
use strict;

my $mydir = 'mysubdir\*';
my @filear = glob($mydir);

my %hash = make_hash(@filear);

sub make_hash { 
    (local $/)=undef; 
    my (@files,%hash); 
    @files = @_; 
          
    foreach my $file ( @files ) { 
     open( my $fh, $file ) or next; 
     $hash{$file} = <$file>; # This line gives "unopened filehandle warning"
    }; 
   return %hash; 
 }

print Dumper \%hash;

##</code><code>##

$VAR1 = {
          'mysubdir\\file1.txt' => undef,
          'mysubdir\\file2.txt' => undef
        };