epubcheck is the actual command, but I have it aliased as epub on one of my machines.
Note: You will have to manually install the command to get an up to date version of it.
epub practical_sorting_in_rust/ --mode exp -v 3.0
epub practical_sorting_in_rust/ --mode exp -v 3.0 --save
Install pandoc and use it to convert your file to plain text.
cat practical_sorting_in_rust/EPUB/ch10.xhtml | pandoc -f html -t plain
With this trick, you can pipe the plain text version to wc and start gathering metrics.
cat practical_sorting_in_rust/EPUB/ch10.xhtml | pandoc -f html -t plain | wc