abusing permission flags to distinguish watched episodes

I do 95% of my file management straight in the terminal using standard coreutils. The remaining 5%, I use vidir.

I also use things like mplayer and mpd to watch episodes and listen to music and podcasts, ergo; no builtin way of marking episodes as watched, as can be found in various gui applications. How, then, would one keep track of what’s watched and what’s not?

The standard LS_COLORS project have a few interesting ways of adding attributes to files and directories with special permission bits set. The most interesting ones are:

SETGID
STICKY
STICKY_OTHER_WRITABLE

All of these can be colored individually, and with the exception of the last one, setting the corresponding bits in the filesystem shouldn’t have any security implications or limitations, assuming a local filesystem where you are the only user.

If a file has the SETGID bit set, when executed, instead of running with the privileges of the group of the user who started it, runs with those of the group which owns the file. In the situation described above, these should be the same in most cases.

If a directory has the STICKY BIT set, all the files in said directory will be modifiable only by their owners. Again, in the situation described above, this isn’t a bad thing.

So, how can we (ab)use this?

Here’s a script called seen that sets the SETGID bit on a file and STICKY on a directory.

#!/usr/bin/perl
# vim:ft=perl:
# abstract: abuse sticky bits etc to mark a movie or show as seen
use strict;
use warnings FATAL => 'all';

if(!@ARGV) {
  use Cwd ();
  push @ARGV, Cwd::abs_path
}

for my $f(@ARGV) {
  if(-f $f) {
    chmod(02740, $f) or warn "chmod: $!\n";
  }
  elsif(-d $f) {
    chmod(01700, $f) or warn "chmod: $!\n";
  }
  else {
    warn "E: $_ is neither a file or a directory\n";
  }
}

Use it like this:

$ mplayer Laleh.S01E01-FOO/Laleh.S01E01-FOO.mkv
$ seen !$

LS_COLORS