LaTeX `\cite{...}` order

citeorder.rb

#!/usr/bin/env ruby

# Author:  Dmitry V. Luciv
# License: WTFPL 2.0 http://wtfpl.net

=begin
When typing many \bibitem's manually, instead of using BibTeX and friends,
it often becomes a pain to sort the bibliography in case when it should
appear in order of citations.

Use it as `citeorder.rb <my_lovely_article.tex >ordering.txt`

This tool is not unique, but at least is very lightweight.
=end

src = STDIN.read

cites = src.scan /\\cite\{(.+?)\}/m
refs = cites.map {|v| v[0].split ','}.flatten.map {|v| v.gsub('%', '').strip}.uniq

refs.each &method(:puts)