You can also use pywallet to dump all the private keys at once and paste the output into the blockchain.info wallet.

https://github.com/jackjack-jj/pywallet

You will need to have Python installed.

dumpwallet "filename"

Dumps all wallet keys in a human-readable format.

Arguments:
1. "filename" (string, required) The filename

Examples:
> bitcoin-cli dumpwallet "test"
> curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "dumpwallet", "params": ["test"] }' -H 'content-type: text/plain;' http://127.0.0.1:8332/
(code -1)