#!/bin/bash
sed -n 's~.*<p>\([^<]*\)</p>.*~\1~p' <<< \
 "<!DOCTYPE html><html><body><h1>Hello!</h1><p>v1.0.4-b</p></body></html>"
 
sed -n -E 's~.*<p>([^<]*)</p>.*~\1~p' <<< \
 "<!DOCTYPE html><html><body><h1>Hello!</h1><p>v1.0.4-b</p></body></html>"