Xclip

xclip is a cli interface for your clipboard.

Documentation

github	https://github.com/astrand/xclip
man xclip	https://man.archlinux.org/man/extra/xclip/xclip.1.en

Usage

# copy 'foo' to selection-buffer (shift+ins)
echo foo | xclip

# copy 'foo' to clipboard (ctrl+v, alt+shift+ins)
echo foo | xclip -selection clipboard  

# print contents of secondary clipboard
xclip -o -selection secondary