#!/bin/bash
s='ptrn: 435324kjlkj34523453
Note1: rtewqtiojdfgkasdktewitogaidfks
Note2: t4rwe3tewrkterqwotkjrekqtrtlltre'
grep -oP '^ptrn:\s*\K.*' <<< "$s"
awk '/^ptrn:/{print $2}' <<< "$s"
sed -n 's/^ptrn:[[:space:]]*\(.*\)/\1/p' <<< "$s"