If you came to this page then probably you have different repositories on bitbucket or guthub and you are trying to work with them using SSH keys from the same Mac.
Do the following
1. Go to the folder ~/.ssh/ (create it if it does not exist yet (mkdir .ssh)) and create new ssh key (do not touch existing id_rsa & id_rsa.pub)
$ cd ~/.ssh/ $ ssh-keygen -f ~/.ssh/key_name_here -C "key_name_here"
it will ask you for passphrase, you can leave it empty. This command will generate private and public keys: “key_name_here” and “key_name_here.pub”
2. Create the file “config” in the same folder (> config) and edit it with your favourite command line editor
Host key_name_here HostName bitbucket.org IdentityFile ~/.ssh/key_name_here
3. Repeat items 1 & 2 for your every next key giving the key new name and alias
4. When you use it, make sure that you are using alias instead of original host name to specify appropriate key name (it is “key_name_here” in the case above), for example, for bitbucket instead of
git clone firstname.lastname@example.org:your/repository_name_here.git
you should use
git clone git@key_name_here:your/repository_name_here.git