#!/bin/bash
s='sdk: ">=0.2.4 <3.1.1"
version: ^2.3.1
sdk: flutter
version 1.0.0+1'
sed -nE 's/.*version:[^0-9]*([0-9][0-9.]*).*/\1/p' <<< "$s"
grep -oP 'version:\D*\K\d[\d.]*' <<< "$s"