Regex: incrimenting/decrimenting

[weberr]

Is there a way to increment/decriment a value before replacing it?
I have a book structured with 90 chapters, each chapter a separate file; however, the chapter numbers are 38-90 (probably from using EpubSplit to break up a 'complete set'.
I would like to renumber the Chapters to be 1-90.
The chapter headings are easy to find: <h2 class="calibre1">Chapter ([0-9]+)</h2>
For replacement is there something akin to <h2 class="calibre1">Chapter \1-37</h2>

[eschwartz]

The calibre editor can do this, with a regex function.

http://manual.calibre-ebook.com/function_mode.html

[weberr]

Originally Posted by eschwartz

The calibre editor can do this, with a regex function.

http://manual.calibre-ebook.com/function_mode.html

Didn't know that the calibre editor had a Regex-Function mode and didn't know there was such a detailed manual for using it. Should have known that calibre had it covered. It always does.

[eschwartz]

It is a relatively new feature.

Although anyone keeping a close eye on certain discussions would have seen Kovid's post indicating that this was going to happen, going back quite some time.

Originally Posted by calibre What's New

Release: 2.11 [21 Nov, 2014]

New Features

• Edit Book: Add a new 'function mode' for the Search and Replace tool
  The function mode allows you to create python functions that run on the results of Search and Replace. This allows you to do arbitrarily powerful text processing. For example, you can automatically fix the case of text, automatically add section number to headings, and so on. For examples and documentation, see: http://manual.calibre-ebook.com/function_mode.html