This uses regex to match all files beginning with id_ and not ending with and dot-suffix, like .pub.
find ~/.ssh -type f -regextype egrep -regex '.*/id_[^.]+$' | xargs ssh-add &> /dev/null The problem with using a for loop, like in the accepted answer, is that you will keep on needing to enter the passphrase even when the same one is used for all keys.