The getblockhash RPC returns the header hash of a block at the given height in the local best block chain.
getblockhash height
*bitcoin-cli help getblockhash
getblockhash height Returns hash of block in best-block-chain at height provided. Arguments: 1. height (numeric, required) The height index Result: "hash" (string) The block hash Examples: > bitcoin-cli getblockhash 1000 > curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "getblockhash", "params": [1000] }' -H 'content-type: text/plain;' http://127.0.0.1:8332/