---
layout: event_detail
title: Collaborative Working Sessions - Filtering diffoscope output
event: hamburg2023
order: 301
permalink: /events/hamburg2023/filtering-diffoscope/
---

Goal: add patterns to filter out some parts of output, or filters to only show some parts of output

Requirements:
- print info that parts output are being ignored
- indicate in return code that files are not identical

A number of options exist:
- `--exclude`
- `--exclude-command=REGEXP`: this skips command matching REGEXP
  (`--exclude-command '^readelf.*gdb_index'`)
  but then diffoscope tries the next command, possibly falling back to hexdump comparison
  
- output formats: `--json`, `--html`, `--htmldir`.
  Multiple output formats can be use together.
  
- `--load-existing-diff FILE`.
  Diffoscope will produce all kinds of output from JSON.
  This can be combined with 'jq' filtering or some other way to filter.

Internally, state is a series of deeply nested dictionaries.
The comparator is called with a paths of keys.

Issues about --exclude* already exist:
https://salsa.debian.org/reproducible-builds/diffoscope/-/issues/130
https://salsa.debian.org/reproducible-builds/diffoscope/-/issues/53
https://salsa.debian.org/reproducible-builds/diffoscope/-/issues/52

Filtering by "output level" is not enough.
For example, in an RPM header, some specific fields should be ignored, but only those.

Idea: provide a command to filter the output using a jq-like path.