problem one, covered in PAR::FAQ

unless(caller)
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Problem two

$source_path = win_path($source_path);
$destination_path = win_path($destination_path);

if (!$destination_path)
{
    $destination_path = $source_path;
}

my @files = <$source_path\\*>;

my %seen;

my $search = 'while (<>) { study;';
$search .= "++\$seen{\$ARGV} if /\\b_$project_id\\b/;\n"; 
$search .= "}";

@ARGV = @files;
undef $/;
eval $search;          
$/ = "\n";
[download]

Don't use string eval, especially for something like that. That should be a single function call, see qr, quotemeta, local