Without resorting to string eval everytime you could use a dispatch table to do this:

{
  # compile each test once...
  my %file_test = map { $_ => eval "sub { -$_ \$_[0] }" }
                   qw(r w x o R W X O e
                      z s f d l p S b c
                      t u g k T B M A C);

  sub FileCheck {
    my($file,$perm,$badness) = @_;
    die "invalid file test" unless exists $file_test{$perm};
    unless ($file_test{$perm}->($file)) {
      if ($badness eq 'die') {
        die "\nError (fatal) accessing $file: $!";
      } elsif ($badness eq 'warn') {
        warn "\nError (non-fatal) accessing $file: $!";
      }
    }
  }
}
[download]

This also makes it relatively simple to create "new" filetests, should you want to...

If you use eval "-$perm... I would advise checking $@ to see if you had an invalid filetest requested.

update: added $_ => so it works. Much apologies. (Also s/exsits/exists/)