How do I pipe terminal standard output (stdout) to the clipboard?

This can be done with either xsel or xclip command line utilities. Since neither program comes with Ubuntu by default you'll need to first install them via Ubuntu Software or the terminal. Here's how in the terminal (but remember you only need one of these two.)

sudo apt install xsel
sudo apt install xclip

Note: If you're using Ubuntu in Windows Subsystem for Linux (WSL) see this other answer instead.

Now some examples. If you want to copy the output of ls to the clipboard here's what you'd do:

With xsel:

ls | xsel -ib

With xclip:

ls | xclip -sel clip

This can of course be utilized for other terminal commands as well. Let's say you want to paste your network info into a help forum.

With xsel:

sudo lshw -C network | xsel -ib

With xclip:

sudo lshw -C network | xclip -sel clip

Make this even easier with a new bash alias!

Edit your ~/.bash_aliases file (if it doesn't exist yet create it first with touch ~/.bash_aliases)

Then add one (depending on which program you decided to go with) of the following:

alias copy='xclip -sel clip'

or

alias copy='xsel -ib'

Then save and close.

Now (after restarting your terminal) you can send standard output to the clipboard just by piping it to 'copy' (or whatever you decide to name your new alias)

For example:

ls | copy

If you are attempting to copy to the clipboard using Ubuntu in Windows Subsystem for Linux (WSL) xsel or xclip will not work unless you are using X Windows as clipboard is only for graphical. However, to pipe terminal standard output to the clipboard in WSL Ubuntu you can use clip.exe. You can then paste into the WSL Ubuntu terminal with standard paste commands and the copied text will be available in Windows as well. For example,

pwd | clip.exe 

will copy the current working directory to the (Windows) clipboard.

This search result appears at the top when looking for ways to copy/paste text in WSL so I think it is worthwhile to mention this so readers do not needlessly install xsel or xclip in Ubuntu and instead use clip.exe.

Found this helpful for using the xclip utility in addition to the answers above. (source)

To Paste (from system clipboard):

xclip -out -sel clip

Demo:

$ echo hello world | xclip -sel clip             copy hello world to clipboard
$ xclip -out -sel clip | tail -f                 can pipe from clipboard
hello world
$ xclip -out -sel clip                           paste defaults to stdout

And thus I added this to my shell profile:

alias copy="xclip -sel clip"
alias paste="xclip -out -sel clip"