如何在X中将文本复制到剪贴板

I was writing a pretty small command line program in Linux and I was thinking that it would be much nicer if it had the ability to copy text directly to the clipboard(not the middle click selection). I looked into it but I couldn't really find a source explaining how to do that with just X11 (without Qt or something). Could someone explain to me how this is done?I was writing a pretty small command line progr