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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