What does it mean to shake hands with an old friend first?

Show friendship. Handshaking is a kind of communication, which can communicate the original feelings and deepen mutual understanding and trust. Old friends shake hands first to show friendship, which can show respect, admiration, congratulations and encouragement of one side. Handshaking is a very common etiquette, which is usually used in occasions such as meeting, parting, congratulations and condolences.