Hi Lawrence,

On Wed, Mar 11, 2020 at 7:56 PM Lawrence Bottorff <borgauf@gmail.com> wrote:

> I read that too, but couldn't fathom what they meant. Still, I'm not sure
> what they mean by "prefix argument."
>

The prefix argument in this case is not so important as the OUTPUT-BUFFER
argument, which you were passing as =t=:

"If OUTPUT-BUFFER is not a buffer and not nil, insert the output in current
buffer after point leaving mark after it."

which is why the output is inserted in the buffer.

And why does (shell-command "uuidgen" t) produces two outputs? For other
> readers, this is what they look like in *scratch*
>
> (shell-command "uuidgen" t)
> 2827
> b5da7e0a-84c0-4db8-91f3-871b681f3022
>

The first number is the return value of shell-command, which is (I think)
the position in the buffer at which the pointer was when the function was
evaluated (or something like this). Here's the output from two consecutive
executions in my *scratch* buffer:

(shell-command "uuidgen" t)
173
5E69575E-2807-40BB-B1FE-10058D3C0666

(shell-command "uuidgen" t)
243
A7FD662E-A752-4E02-B4E0-A3E48CC7E7AB

The "173" happens to appear at point position 173 in the buffer, and same
for the 243 (you can verify this with "C-u C-x =").

Hope this helps!

--Diego