Either learn how to use the debugger or Data::Dumper. I've modified your code to dump some values. They are not quite what you expect!

#!/usr/bin/perl -w

use Data::Dumper;
use strict;

my $dir = 'C:\Users\ZB\Desktop\Text Files';
$dir = 'c:';
opendir (DIR, $dir) or die "cannot opendir $dir";

foreach my $file (readdir(DIR))
{
    warn Data::Dumper->Dump([\$file],[qw(*file)]).' ';
    &process_file ($file);
}

sub process_file
{
    warn Data::Dumper->Dump([\@_],[qw(*_)]).' ';
    my $line = @_;
    warn Data::Dumper->Dump([\$line],[qw(*line)]).' ';
    my @array = split(/ /, $line);
    print "$#array\n";
}

closedir (DIR);
[download]

And this produces:

Microsoft Windows [Version 6.1.7601]
Copyright (c) 2009 Microsoft Corporation.  All rights reserved.

C:>perl opendir.pl
$file = \'.';                      # This is '.'
  at opendir.pl line 12.
@_ = (                             # Your sub get an array containing 
+'.'
       '.'
     );
  at opendir.pl line 18.
$line = \1;                        # but $line is 1 (the length of @_)
+ ...
  at opendir.pl line 20.           # what you really wanted is my ($fi
+lename) = @_; # This is the name of the file that needs to be opened/
+read/closed
0
$file = \'..';
  at opendir.pl line 12.
@_ = (
       '..'
     );
  at opendir.pl line 18.
$line = \1;
  at opendir.pl line 20.
0
$file = \'MyOpen(0).pl';
  at opendir.pl line 12.
@_ = (
       'MyOpen(0).pl'
     );
  at opendir.pl line 18.
$line = \1;
  at opendir.pl line 20.
0
...
[download]