Bash script

#!/bin/bash

if [ $# -eq 0 ]
then
  echo "Parameters required!"
  exit 1
fi

book=$1
bookext=${book##*.}
bext=${bookext^^}

if [ $bext = 'PDF' ]
then
  ebook-convert "$1" "${1%.*}.epub" --no-image --unwrap-factor=0.1
  exit 1
fi

ebook-convert "$1" "${1%.*}.epub"