xsel

X11 selection and clipboard manipulation tool. More information: https://manned.org/xsel.

• Use a command's output as input of the clip[b]oard (equivalent to Ctrl + C):
  echo 123 | xsel -ib
• Use the contents of a file as input of the clipboard:
  cat {{path/to/file}} | xsel -ib
• Output the clipboard's contents into the terminal (equivalent to Ctrl + V):
  xsel -ob
• Output the clipboard's contents into a file:
  xsel -ob > {{path/to/file}}
• Clear the clipboard:
  xsel -cb
• Output the X11 primary selection's contents into the terminal (equivalent to a mouse middle-click):
  xsel -op