title_body: how to convert markdown with sub-markdowns to ebook main.md contain sub-mds:
  
  main.md
  
  1. [1 - ](1.md)
  1. [2 - ](2.md)
  1. [3 - ](3.md)
  1. [4 - ](4.md)
  1. [5 - ](5.md)
  1. [6 - ](6.md)
  
  
  I use calibre command:
  
  ebook-convert main.md main.epub
  
  
  But only the content of main.md is wrote to epub.
upvoted_answer: I found two things.
  
  For me the link has to be written '( ./6.md )' with a space before and after the file specification.
  
  Then I found the ebook-convert app wants html files for inputs.
  It complains that the inputs are "binary"