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Date: Wed, 4 Apr 2007 19:54:52 -0600
From: "Morgan Gangwere" <0 DOT fractalus AT gmail DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: Escape colour codes
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"and this children is why we stick to rxvt and puttyCyg!"

On 4/4/07, Matthew Woehlke <mw_triad AT users DOT sourceforge DOT net> wrote:
> Eric Blake wrote:
> > The bug in all three of these programs is that they are adding spurious \1 into
> > the string passed to readline.  When you call readline("\001\001invisible\001
> > \002plain"), then readline assumes that anything between the FIRST \001 and the
> > \002 is invisible (ie. special to the terminal instead of literal output).  So
> > readline thinks that it should PRINT the invisible string "\001invisible\001"
> > special to the terminal, followed by the visible string "plain".  However, as
> > you noticed, \001 is NOT special to the cmd.com terminal, and results in a
> > smiley face, and readline is now thoroughly confused (it thinks it is waiting
> > for input on position 6, but in reality it is waiting for input on position 8,
> > because you printed literal characters while claiming they were invisible).
> >
> > Bash, on the other hand, DOES map \[ to the sequence '\001\001' inside of
> > parse.y's decode_prompt_string(), BECAUSE it later calls expand_prompt_string()
> > to get rid of the extra \001.  It needs to do this so that it can support
> > PS1='$(foo)' (the prompt is the expansion of command foo), and needed a way to
> > tell \[ and \] in PS1 apart from literal \001 and \002 resulting from the
> > expansion of other elements in the prompt string.  When the prompt is finally
> > expanded and ready to hand to readline, the extra \001 _used by bash_ is gone,
> > leaving only the SINGLE \001 _used by readline_.  In other words, the common
> > bug in all three programs you mentioned is that they copied bash's escape
> > sequences, but NOT bash's round of internal expansion, prior to calling
> > readline.  The comment in the lftp sources was rather revealing - if the coder
> > didn't know why bash used an extra \001, they shouldn't have copied that.
>
> Given that three separate programs had *the same bug*, and given that
> bash is perhaps the most visible readline user, maybe it would be
> worthwhile to mention (briefly) in readline's doc to *not* copy bash's
> extra \001 in your own implementation? :-)
>
> Anyway, I'm glad this was resolved without my (mis)help interfering too
> much. :-)
>
> --
> Matthew
> "Will somebody get this walking carpet out of my way?!" -- Princess Leia
> Organa
>
>
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>


-- 
Morgan gangwere

"Space does not reflect society, it expresses it." -- Castells, M.,
Space of Flows, Space of Places: Materials for a Theory of Urbanism in
the Information Age, in The Cybercities Reader, S. Graham, Editor.
2004, Routledge: London. p. 82-93.

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