.agent_loader

#!/bin/bash

cd "$(dirname "$0")"
GIT_KEYS="gitkey_*"                                                 # my git keys are always loaded but agent forwarding is limited specific Hosts
SSH_KEYS=""                                                         # my ssh keys are never loaded
SSH_AGENT_PID=1                                                     # `kill -0 1` will always fail for non-root
SSH_AGENT_ENV=".agent_env"

[ -f "${SSH_AGENT_ENV}" ] && source "${SSH_AGENT_ENV}" > /dev/null  # load latest known agent pid
kill -0 $SSH_AGENT_PID 2>/dev/null && return                        # and stop here if still running (do not 'exit' because file may be source'd)

echo "Loading SSH Agent..."
chmod -f 600 "${SSH_AGENT_ENV}"
/usr/bin/ssh-agent > "${SSH_AGENT_ENV}"                             # overwrite latest (not running anymore)
source "${SSH_AGENT_ENV}" > /dev/null

for key in $GIT_KEYS; do /usr/bin/ssh-add "$key"; done

.bashrc

# ...stuff before...

for i in ~/.bash_aliases ~/.ssh/.agent_loader
do
  [ -f "$i" ] && source "$i"
done

# ...stuff after...

gitkey_gen_example.sh

#!/bin/bash

ssh-keygen -f ~/.ssh/gitkey_git.example.com -P randompass -t ed25519 -C "username@provider.com for git.example.com"