gistfile1.txt

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" 
   "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
  <dict>
    <key>Label</key>
    <string>org.gnupg.gpg-agent</string>
    <key>ProgramArguments</key>
    <array>
      <string>start-gpg-agent</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
  </dict>
</plist>

gistfile2.txt

if test -f $HOME/.gpg-agent-info && 
  kill -0 `cut -d: -f 2 $HOME/.gpg-agent-info` 2>/dev/null; then

   . "${HOME}/.gpg-agent-info"
  export GPG_AGENT_INFO
  export SSH_AUTH_SOCK
  export SSH_AGENT_PID
else
  gpg-agent --daemon --enable-ssh-support \
    --write-env-file "${HOME}/.gpg-agent-info"
fi

export GPG_TTY=$(tty)