This function calls the command ebook-convert in Calibre (https://calibre-ebook.com) to convert e-books.

calibre(input, output, options = "")

## Arguments

input The input filename. The output filename or extension (if only an extension is provided, the output filename will be the input filename with its extension replaced by output; for example, calibre('foo.epub', 'mobi') generates foo.mobi). A character vector of additional options to be passed to ebook-convert.

## Value

The output filename.