Issue 7059 - Modify fldiff so it can handle multiple files

README.md

 # python-abp
 
 This repository contains a library for working with Adblock Plus filter lists
 and the script that is used for building Adblock Plus filter lists from the
 form in which they are authored into the format suitable for consumption by the
 adblocking software.
 
 ## Installation
 
 Prerequisites:
@@ skipping 70 matching lines @@
 
     $ flrender easylist.txt output/easylist.txt
     Unknown source: 'easylist' when including 'easylist:easylist/easylist_gener
     al_block.txt' from 'easylist.txt'
 
 You can clone the necessary repositories to a local directory and add `-i`
 options accordingly.
 
 ## Rendering diffs
 
-A diff allows a client running ad blocking software such as Adblock Plus to update
-the filter lists incrementally, instead of downloading a new copy of a full list
-during each update. This is meant to lessen the amount of resources used when updating
-filter lists (e.g. network data, memory usage, battery consumption, etc.), allowing 
-clients to update their lists more frequently using less resources.
+A diff allows a client running ad blocking software such as Adblock Plus to
+update the filter lists incrementally, instead of downloading a new copy of a
+full list during each update. This is meant to lessen the amount of resources
+used when updating filter lists (e.g. network data, memory usage, battery
+consumption, etc.), allowing clients to update their lists more frequently using
+less resources.
 
-Python-abp contains a script that produces the diff between two versions of a
-filter list called `fldiff`:
+Python-abp contains a script called `fldiff` that will find the diff between the
+latest filter list, and any number of previous filter lists:
 
-    $ fldiff base.txt latest.txt output.txt
+    $ fldiff -o diffs/easylist easylist.txt archive/*
 
-This will produce a diff that shows how a client may get from `base.txt` to
-`latest.txt`, and write the output to `output.txt`. The output argument is
-optional. If ommitted, the data will be written to `stdout`.
+where `-o diffs/easylist` is the (optional) output directory where the diffs
+should be written, `easylist.txt` is the most recent version of the filter list,
+and `archive/*` is the directory where all the archived filter lists are. When
+called like this, the shell should automatically expand the `archive/*`
+directory, giving the script each of the filenames separately.
 
-The script produces three types of lines, as specified in the [technical specification][5]:
+In the above example, the output of each archived `list[version].txt` will be
+written to `diffs/diff[version].txt`. If the output argument is omitted, the
+diffs will be written to the current directory.
+
+The script produces three types of lines, as specified in the [technical
+specification][5]:
+
 * Special comments of the form `! <name>:[ <value>]`
 * Added filters of the form `+ <filter-text>`
-* Removed filter of the form `- <filter-text>`
+* Removed filters of the form `- <filter-text>`
+
 
 ## Library API
 
 Python-abp can also be used as a library for parsing filter lists. For example
 to read a filter list (we use Python 3 syntax here but the API is the same):
 
     from abp.filters import parse_filterlist
 
     with open('filterlist.txt') as filterlist:
         for line in parse_filterlist(filterlist):
@@ skipping 78 matching lines @@
 
 Now you can use the functions with `abp$functionname`, e.g. 
 `abp.line2dict("@@||g.doubleclick.net/pagead/$subdocument,domain=hon30.org")`
 
 
  [1]: https://adblockplus.org/filters#special-comments
  [2]: http://pytest.org/
  [3]: https://tox.readthedocs.org/
  [4]: https://github.com/numpy/numpy/blob/master/doc/HOWTO_DOCUMENT.rst.txt
  [5]: https://docs.google.com/document/d/1SoEqaOBZRCfkh1s5Kds5A5RwUC_nqbYYlGH72sbsSgQ/