Calibre Book Export is a wrapper around the "calibredb export" that intelligently manages an exported collection of books for using a tool like Rsync, Unison, or FolderSync on Android (this author's current toolset) to copy the collection elsewhere.

• Maintains an export directory based on tags or custom column data in the Calibre database.

• Does not change timestamps or other filesystem metadata on books that have not changed since the last export. (Does not depend on dates in the Calibre DB, exports all marked books and uses file-size comparisons.)

• Fixes up exported filenames to remove Goofy Characters That Shouldn't Be In Filenames.

• Uses an optional Genre (or other user-specified column) to organize books by sub-folders in the export directory.

Tested with Calibre v1.26 to v1.27. calibre-book-export itself is a Bash script, and it relies on Rsync. (My apologies to Windows folks, but this is the world I live in.)

The author wants certain books in his Calibre library to automagically appear on his Android tablet, by way of sychronizing a folder from his personal webserver. Calibre Book Export, run on the workstation where Calibre is installed, searches the Calibre DB for books tagged/flagged as "export" (he uses a custom column named "Fav" to keep track of things to read next, and one of the values possible in this column is "export"), and exports the marked books into a temporary directory. CBE then uses Rsync to sync this temporary directory to the "real" target directory. That target directory is later Rsync'd by a cronjob (not part of this package) to the remote webserver directory.

The key element here is that tempdir-to-target Rsync is set to not update timestamps and to delete missing files in the target. This means it only changes files which have actually changed, and doesn't change timestamps unnecessarily. This is important because some sync tools rely entirely on date to tell that a file has changed, and even Rsync defaults to depending on the date.

In addition to the above, Calibre Book Export looks at the Genre column (another custom column, with genre entries like Tech.Programming.Bash) and makes sub-directories in the target directory based on the first two elements of the first genre (books/Tech.Programming), filing all the exported books appropriately.

Redundant Export: At the moment, calibre-book-export exports every book marked for export and then does the comparison with the target directory. This works well for small export sets, but may be cumbersome to, say, export all the books from a large database on a nightly basis. It will work, and if it happens when you're asleep you likely won't notice. But it will go through the motions of writing out every book even if no book has changed in weeks.

This is because the script doesn't care what is in the Calibre DB except that a book is flagged for export, and the optional value to file the book in a sub-directory. calibre-book-export keeps no state of its own, beyond the exported book directory. Replacing a book format within a book record does not update the "Date" meta-data (which normally reflects when the book record was created). So it's not a reliable indicator of whether a book has changed or not, even if I thought it worthwhile to track the state necessary to determine if a book has already been exported or not.

If there is any demand for it, I'll consider adding it. But to reliably detect book changes probably means hunting down the book in the Calibre library directory and checking the date on the actual file. Finding that book likely will depend on reading the Calibre SQLite database directly to read the book path. That's a lot of work and debugging to avoid having the script just write everything out every night.

Optionally, calibre-book-export could keep track of what books were marked for export last time and only export books that were marked for export since the last run. This would work for new books, which has been the bulk of my usage, but it wouldn't work for books that have been updated. (That happens when beta copies are revised, or books get updated with errata, etc. I do deal with this, and having updated books reexported is a necessary feature for me.)