On Sat, 6 Jul 2019 at 12:32, Steve Mynott <steve.mynott@gmail.com> wrote:
> I did a simple "strace dpkg -S /usr/bin/411toppm|grep open" and looked at some of the paths and came up with
>
> basename `grep -rl "^/usr/bin/411toppm$" /var/lib/dpkg/info` .list

Interesting, thanks. If I understand correctly this would only work on
the live system (or at least a similar system with the same packages
installed) but I could, at a push, look at the files in the
var/lib/dpkg/info directory in the tarball. Whilst that would be slow
if done for each file separately, I could just extract and parse all
the .list files in that directory (of the tarball) up front which
would be pretty workable.

> I've tended to use rsync -n to compare directories of files and a scripting language (or go) is probably a better tool than shell.

I'm working with a python script that can directly parse the
compressed tarball (I found a sample script which could calculate
checksums of all files in a tarball pretty quickly which I'm using as
a base, because "tar -jtv" doesn't give enough information to detect
if a file has changed), so my intention is to build on that. Parsing
the .list files on the fly should be an easy add.

And in fact, I can compare just the list of .list files in that
directory to get a diff of installed packages, so that's a good start.
(But I do need to then exclude the files from each package from
further comparisons, so I'd still need to parse them.)

[Actually on a quick dig, the .md5sums files are probably more useful
than the .list files for my purposes.]

Thanks for that starting point.
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