#!/bin/bash
a='
{
"kind": "yt#playlistItemListResponse",
"etag": "\"hvjhjjvhj_hvhv/jvjhvjhvj-dd\"",
"nextPageToken": "CDIQAA",
"pageInfo": {
"totalResults": 199,
"resultsPerPage": 50
},
"items": [
...
'
echo "$a" | grep nextPageToken | cut -d '"' -f4
IyEvYmluL2Jhc2gKCmE9Jwp7CiAia2luZCI6ICJ5dCNwbGF5bGlzdEl0ZW1MaXN0UmVzcG9uc2UiLAogImV0YWciOiAiXCJodmpoamp2aGpfaHZodi9qdmpodmpodmotZGRcIiIsCiAibmV4dFBhZ2VUb2tlbiI6ICJDRElRQUEiLAogInBhZ2VJbmZvIjogewoJInRvdGFsUmVzdWx0cyI6IDE5OSwKCSJyZXN1bHRzUGVyUGFnZSI6IDUwCiB9LAogIml0ZW1zIjogWwogLi4uCicKZWNobyAiJGEiIHwgZ3JlcCBuZXh0UGFnZVRva2VuIHwgY3V0IC1kICciJyAtZjQ=