best script ever, place it as `~/bin/clip`

clip.sh

#!/bin/bash
# Linux version
# Use this script to pipe in/out of the clipboard
#
# Usage: someapp | clipboard     # Pipe someapp's output into clipboard
#        clipboard | someapp     # Pipe clipboard's content into someapp
#

if command -v xclip 1>/dev/null; then
    if [[ -p /dev/stdin ]] ; then
        # stdin is a pipe
        # stdin -> clipboard
        xclip -i -selection clipboard
    else
        # stdin is not a pipe
        # clipboard -> stdout
        xclip -o -selection clipboard
    fi
else
    echo "Remember to install xclip"
fi