Is there any way to auto-gererate an index for the
makeidx package? I've written ~270 pages and didn't think of adding
Do I really need to go over everything and add
Unfortunately yes. At best even if you write a script to automate it you will end up with a concordance, and a concordance is not an index.
In my opinion it is actually better to postpone the writing of the index to the time the book is almost ready. Writing an index is an art and most publishers employ "human indexers" to write an index that is useful and serves its function.
Since luckily, you missed it the first time round this is a good time to give it a bit of a thought and planning, before you delve into it.
The most important points to consider when developing an index, is categorization and consistency. Think of the likely readers of your book (or even the older you that will forget what the younger you wrote) and provide headings that are likely to be used when searching for information. Consider for example a historical book, describing early ships and their trade routes. It can be meaningless for example to just index the ship name by one word. Consider the following MWE:
I have used a heading to categorize the ship as a steam ship (you can add macros as necessary) and provided a second one to classify Melbourne as a port. By creating a number of commonly used categories around your topic you can also ensure that you have a good classification system as well as providing consistency. As you might have probably noticed the ship's name is typeset in italics, to comply with the Oxford Style Guide and by creating a macro both the indexing as well as the typesetting are done correctly and efficiently.