How to copy from console/terminal/file to X clipboard in Linux

We need to use xclip package which is command line interface to X selections.

Install:

sudo apt-get update
sudo apt-get install -y xclip

We can copy file contents to clipboard, for example:

xclip -i < .ssh/id_rsa.pub

Now file contents are in system clipboard and we can use Ctrl + V to paste it anywhere.