You can use a bash script to import multiple keys, first of all put all those keys on a text file and then you can run something like:
for a in $(cat keys.txt)
do
bitcoin-cli importprivkey $a
done
By default, Bitcoin Core will rescan whole blockchain to find all transaction related to the imported private key. If OP insist use Bitcoin Core, i think skip scanning when import private key & perform scan after all private keys are imported is more efficient.
for a in $(cat keys.txt)
do
bitcoin-cli importprivkey $a "" false
done
bitcoin-cli rescanblockchain