What is :silent !echo doing? Why does it get the cursor to the top?

Question

This question on StackOverflow triggered my curiosity.

What does :silent !echo doing?

The first time I saw something like :excommand !shellcommand was when I was looking for a way to save a read-only file from within a non-sudo Vim session. Indeed I found the famous How does the vim “write with sudo” trick work?. In that case, however, it's "easy" to search for :help :w and scroll down a bit find the entry :[range]w[rite] [++opt] !{cmd} which describes the meaning of that !.

In the case of :silent, instead, doing :help :silent doesn't bring anywhere the question mark is used after a space and before {command}.

My understanding is that :silent !echo is working mostly like :!echo but without showing any of the output or of the underlying shell, and sending the cursor to the top of the screen. I've recorded a screencast for reference. (NOTE: All those horizontal lines that you see happen to be present only in the screencast, for some reason, there's no such a thing in my system.)

This question seems related.

Answer 1

Well, there's :silent:

:sil[ent][!] {command}  Execute {command} silently.  Normal messages will not
                        be given or added to the message history.

and there's :!

:!{cmd}         Execute {cmd} with the shell.  See also the 'shell'
                and 'shelltype' option.

Your hunch is mostly correct; I'm not sure why the cursor goes to the top of the screen, but it's probably because the command outputs a drawing code (termcap stuff), which vim is also using to draw on the screen.