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Example: perms

    #! /usr/bin/perl -w
    #
    # perms - complain about files that students can inappropriately read.
    #
    # We take the "all is forbidden unless permitted" approach.
    # Complain about any publically readable or writable file unless
    # it's in a directory with a ".public" flag file.

    use strict;
    use File::Find;

    find {wanted => \&wanted, no_chdir => 1},
          glob("~applin"),
          glob("~cs155"),
          glob("~cs156"),
          glob("~cs157"),
          glob("~cs253");

    sub wanted {
            my @statbuf = stat($_);
            my $mode = $statbuf[2] || 0;
            my $r = $mode & 044;
            my $w = $mode & 022;
            my $x = $mode & 011;

            if (-d) {
                    $File::Find::prune = 1          # Give up on this directory
                            unless -r && -x;        #   if we can't search it.
                    $File::Find::prune = 1          # Give up on this directory
                            unless $r && $x;        #   if nobody can search it.
                    $File::Find::prune = 1          # We don't care about this dir
                            if -e "$_/.public";     #   if it's marked as public.
                    return;
            }

            return if m!/\.[^/]+$!;                 # We don't care about .files

            ls($_)                                  # Show permissions and filename
                    if $r || $w;                    #   if publically accessible
    }


    # Emulate the ls -l command

    sub ls {
            my ($file) = @_;
            my $cmdout = `/bin/ls -l "$file"`;      # for the -rwxr-xr-x part
            printf "%.10s %s\n", $cmdout, $file;    # Show permissions and filename
    }