Re: [PATCH] Try URI quoting for embedded TAB and LF in pathnames

From: Linus Torvalds <torvalds@osdl.org>
Date: Oct 12, 2005, 19:52 UTC
Message-ID: <Pine.LNX.4.64.0510121220230.15297@g5.osdl.org>
In-Reply-To: <Pine.LNX.4.63.0510121452030.23242@iabervon.org>

On Wed, 12 Oct 2005, Daniel Barkalow wrote:

> 
> I think it's actually sufficient to escape 0x00-0x1f and 0x7f; those 
> ranges are both easy

They are indeed easy.

>		 and, as far as I can tell, include all of the control 
> characters that do annoying things.

Nope. The traditional vt100 escape sequence is "ESC" followed by a character to indicate the type of sequence (the most common one is '['). That's all 7-bit and fine.

HOWEVER, they made the 8-bit extension be such that any of these vt100 begin sequences where the second character is in the appropriate range can be instead shortened by one character, by instead using a single 8-bit character of "0x80+(char-0x40)". Ie the traditional "ESC + '['" (\x1b\x5b) can also be written as a single '\x9b' character, aka CSI.

In other words, 0x80-0x9f are _all_ just vt100 shorthand for ESC+'@' through ESC+'_'.

(I guess it's not strictly "vt100" any more - it's the extended vt220 format).

> I think escape, backspace, delete, and 
> bell are the only ones we'd rather the terminal not get; beyond that, 
> patches with screwy filenames look screwy, but don't screw up anything 
> outside of the filename.

Try this on a (non-UTF-8) xterm:

	echo -en '\x9b5B---\x9b1A---\x9b4A\r'

and it should do:
 - move cursor 5 lines down
 - print "---"
 - move cursor 1 line up
 - print "---"
 - move cursor 4 lines up
 - return carriage to beginning.

In other words, your screen should end up looking something like this:

	[torvalds@g5 ~]$ echo -en '\x9b5B---\x9b1A---\x9b4A\r'
	[torvalds@g5 ~]$
	
	
	
	   ---
	---

where that "staircase" of two "---" things was done with cursor movements.

And that's a _benign_ sequence. You can do all kinds of funky stuff that really screws up the user experience. Including have the thing echo keys to you that you didn't type:

	echo -en '\x9b5n'

or lock the keyboard (I don't think any of the terminal emulators implement the latter, or some of the other stranger sequences - things to do double-wide characters etc).

			Linus

PS. You can do all the same in UTF-8 one, but then you'll have to add a \xc2 before the \x9b:

	echo -en '\xc2\x9b5B---\xc2\x9b1A---\xc2\x9b4A\r'

etc..