I know about pywallet, about this modification for bitcoind, but what is a simple way to merge two wallets, or export a list of private keys and addresses of all of wallets from litecoin, dogecoin, bitcoin, quark, et cetera?
Latest versions of the reference Bitcoin implementation have the 'dumpwallet' RPC command, which dumps a human-readable list of all of your private keys.
The format is simple: just comment-lines (starting with #) or lines that are the private key (plus metadata about the key). So to combine keys from several wallets you would:
The last step will take a while as the blockchain is scanned for transactions to/from the imported private keys (concatenating several wallet keys together in step 3 saves time over repeatedly dumping/importing).
A php or python or bash script that did all of the starting/stopping/concatenating either using the JSON/RPC interface or bitcoin-cli would be spiffy. Extra credit if it noticed which wallets were locked and prompted for passphrases....