Cloning and pushing code would often fail when we have multiple git accounts on a single machine. A little setup and organization would help here.

Follow the below steps to setup multiple git accounts on macOS.

Create SSH keys for the accounts
Add the SSH keys to the ssh agent
Add the respective public SSH keys to the Git websites
Create config file on your Mac
Make an Account Git Default
Use Git with Non-default or Secondary Accounts
Push from already cloned repositors

1. Create SSH keys for the accounts

In the below commands, -C is for comment, -f for output file name.

Best practice for -f option is to use github-{GIT_ACC_NAME} to identify keys later, to avoid confusion.

cd ~/.ssh
$ ssh-keygen -t rsa -C "emailid_one_github@email.com" -f "github-account1"
$ ssh-keygen -t rsa -C "emailid_two_github@email.com" -f "github-account2"
$ ssh-keygen -t rsa -C "emailid_three_bitbucket@email.com" -f "bitbucket-account-2"

2. Add the SSH keys to the `ssh` agent

Add your keys to ssh agent by alternative set of commands mentioned below. When you use Alternate-1 that uses option -K, you might get the below warning. Still, the key gets added.

WARNING: The -K and -A flags are deprecated and have been replaced
         by the --apple-use-keychain and --apple-load-keychain
         flags, respectively.  To suppress this warning, set the
         environment variable APPLE_SSH_ADD_BEHAVIOR as described in
         the ssh-add(1) manual page.

Go ahead, run these commands. Shall you see any such warning, replace -K with --apple-use-keychain.

2.1 Alternate 1:

$ ssh-add -K ~/.ssh/github-account1
$ ssh-add -K ~/.ssh/github-account2
$ ssh-add -K ~/.ssh/bitbucket-account-2

2.2 Alternate 2:

$ ssh-add --apple-use-keychain ~/.ssh/github-account1
$ ssh-add --apple-use-keychain ~/.ssh/github-account2
$ ssh-add --apple-use-keychain ~/.ssh/bitbucket-account-2

3. Add the respective public SSH keys to the Git websites

Copy your SSH keys into clipboard with the below command.

// Run this command for respective keys
$ pbcopy < ~/.ssh/github-{ACC}.pub

Follow the below links to add SSH keys on the website.

4. Create config file on your Mac

Create a file with name config, and edit.

vi ~/.ssh/config

-- OR --

open -e ~/.ssh/config

Now, add the below content to your config file.

#Github account1
Host github.com-{GIT_ACCOUNT_NAME_1}
    HostName github.com
    User git
    IdentityFile ~/.ssh/github-account1

#Github account2
Host github.com-{GIT_ACCOUNT_NAME_2}
    HostName github.com
    User git
    IdentityFile ~/.ssh/github-account2

#Bitbucket account2
Host bitbucket.org-{BitB_ACCOUNT_NAME}
    HostName bitbucket.org
    User git
    IdentityFile ~/.ssh/bitbucket-account-2

5.Make an Account Git Default

git config --list lists yours default global git configuration values. If you want to change, you can change with the below commands.

$ git config --global user.name "Chandra"
$ git config --global user.email "emailid@mail.net"

6. Use Git with Non-default or Secondary Accounts

Referring the config file, you can use this command to use a particular git account.

$ git clone git@github.com-{GIT_ACCOUNT_NAME_1}:{-{GIT_ACCOUNT_NAME_1}}/{REPO_NAME}.git

An example would be:

$ git clone git@github.com-chandra:developerchandra/sample-project.git

Now, you might not want to use global configurations (email and name) for every repo that you checkout. It would be better to change git config for the repositories you check out. So, you can run the following commands once you check out a repo.

$ git config user.email "{EMAIL FOR ACCOUNT ONE}"
$ git config user.name "{YOUR NAME FOR ACCOUNT ONE}"

$ git config user.email "{EMAIL FOR ACCOUNT TWO}"
$ git config user.name "{YOUR NAME FOR ACCOUNT TWO}"

7. Push from already cloned repositors