Reproducible builds

Some of the document formats pandoc targets (such as EPUB, docx, and ODT) include build timestamps in the generated document. That means that the files generated on successive builds will differ, even if the source does not. To avoid this, set the SOURCE_DATE_EPOCH environment variable, and the timestamp will be taken from it instead of the current time. SOURCE_DATE_EPOCH should contain an integer unix timestamp (specifying the number of seconds since midnight UTC January 1, 1970).

Some document formats also include a unique identifier. For EPUB, this can be set explicitly by setting the identifier metadata field (see EPUB Metadata, above).