epubcount.sh

#! /usr/bin/env sh
# usage: ./epubcount.sh <epubfile>
# remember to `chmod +x epubcount.sh`

IFS=$'\n' #change the internal field separator, otherwise file with spaces will fail.
mkdir temporary/ #use a temporary directory
unzip -jq $1 *html -d temporary/ #unzip all xhtml/html files of the epub archive
cd temporary/ #change directory
cat *html > out.html #concatenate all html
count=`cat out.html | sed 's/<[^<]*>/ /g' | wc -w` #count the words of the concat'd file, excluding tags.
echo $1 ": " $count
cd ..
rm -rf temporary/ #we can trash the directory