Start CosmOS with a script, and let a script hold its tongue

Three things scripts wanted, and they are one thing: a machine that can
have a face.

/System/Boot/startup.sh runs before anybody can type. Every way of reaching
the prompt for the first time goes through it, including the one where
there is no disk - in which case there is nothing to find and nothing is
said. A MISSING one is ordinary and silent, because a clean install has
none and a machine that complained every boot about a file nobody wrote
would be teaching its owner to ignore it. One that is THERE and does not
begin with #! is the other case entirely: somebody meant that to run.

#quiet stops each line being echoed, #loud puts it back. The prompt and the
echo go together, because together they are what makes a script look like
typing, so a quiet script gets neither and what it prints is all that
appears. A nested script inherits quiet - a build that asked for it meant
its helpers too - and gets its own setting back when the helper returns.
Anything else beginning with # is handed to the shell, which does not know
it and stops the script, because a script that asked for something this
shell cannot do should not carry on as though it had been given it.

clear empties the screen, which the console has been able to do since
before there was a screen to do it on.

THE PROMPT IS NOW SAID BY WHOEVER SUPPLIES THE LINE. It used to be said at
the top of the loop, which is a decision made before the line is read and
an answer not known until after - and it was wrong at both ends. #quiet is
itself a line, so its prompt went out before anything knew to stay silent;
and the line after a quiet script's last one comes from the console, having
already been denied one. Off by exactly one line in opposite directions. A
first attempt at this remembered whether the prompt had been skipped, which
worked and was a flag standing in for a structure. The monitor's assembler
prints a prompt of its own, so it reads through shellReadRaw, which is the
same source without one.

One admission. Handing the console its prompt back when a quiet script
ended was a real fix when I wrote it and stopped being one an hour later,
because the restructure above means the console's own path prompts whatever
the flag holds. The comment claimed it fixed something. Breaking it on
purpose changed nothing, which is how that was found, and it is now a
comment saying so instead of a line pretending to work.

The startup fixture ends QUIET on purpose: nothing puts the flag back when
the outermost script finishes, so a script ending #loud would have tested
the easy half.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW

Programs/CosmOS/README.md

@@ -156,6 +156,48 @@ comment that only the kernel looks at, while here the shell requires it.
 **Each line is echoed as it runs**, after the prompt, so that a script reads exactly like
 somebody typing it and a script that stops says where.
 
+**`#quiet` turns that off and `#loud` turns it back on.** The prompt and the echo go together,
+because together they are what makes a script look like typing - so a quiet script gets
+neither, and what it prints is all that appears. That is for the scripts whose own output is
+the point, where prompts interleaved with the message are just in the way:
+
+```
+#! script
+#quiet
+clear
+echo Segan Voyager
+echo CosmOS ready.
+```
+
+A nested script inherits quiet from the one that started it, on the grounds that a build which
+asked for quiet meant its helpers too, and gets its own setting back when the helper returns.
+A script started from the prompt always begins loud.
+
+**Anything else beginning with `#` is handed to the shell**, which does not know it, says so,
+and stops the script. A script that asked for something this shell cannot do should not carry
+on as though it had been given it.
+
+## Starting Itself:
+
+If `/System/Boot/startup.sh` is there, it runs before anybody can type - every way of reaching
+the prompt for the first time goes through it, including the one where there is no disk, in
+which case there is simply nothing to find.
+
+**A missing one says nothing**, because a clean install has none and a machine that complained
+every boot about a file nobody wrote would be teaching its owner to ignore it. A file that *is*
+there and does not begin with `#!` is the other case entirely - somebody meant that to run - so
+it says so and carries on to the prompt.
+
+Between them, `startup.sh` and `#quiet` are how a machine gets a face:
+
+```
+#! script
+#quiet
+clear
+echo Segan Voyager
+echo CosmOS ready.
+```
+
 **A script stops at the first line that does not work.** A build whose first step failed and
 whose second step ran anyway produces something wrong and reports success, which is the whole
 reason the shell now remembers whether a line worked. What counts as not working is a command
@@ -191,6 +233,7 @@ CosmOS currently provides these built-in commands:
 | `run [words]` | Start the loaded application and make the rest of the line available to it as an argument. |
 | `do <script>` | Run the lines in a file as though they had been typed. See Scripts. |
 | `echo [words]` | Say the rest of the line, or a blank line with nothing after it. |
+| `clear` | Empty the screen. |
 | `cd [path]` | Go to a directory, or to the root with nothing after it. |
 | `mkdir <path>` | Make a directory. |
 | `rmdir <path>` | Remove one, if it is empty. |