On Wed, Oct 28, 2015 at 8:55 AM, Chet Ramey <chet.ra...@case.edu> wrote:
> On 10/27/15 5:02 PM, Greg Wooledge wrote:
> > I decided to play around with the ${var@P} expansion in 4.4-beta.
> >
> > imadev:~$ red=$(tput setaf 1) reset=$(tput sgr0)
> x='\[$red\]\u\[$reset\]@\h:\w\$ '; printf %s "${x@P}" | od -t x1
> > 0000000 1 1b 5b 33 31 6d 2 77 6f 6f 6c 65 64 67 1 1b
> > 0000020 5b 6d f 2 40 69 6d 61 64 65 76 3a 7e 24 20
> > 0000037
> >
> > I don't think the "1" and "2" bytes should be printed. They're for
> > internal use only, even if they're usually invisible.
>
> That's what the \[ and \] escape sequences expand to and use to
> communicate information to readline about invisible characters in the
> prompt (RL_PROMPT_START_IGNORE and RL_PROMPT_END_IGNORE). If you want to
> use the expansion of ${var@P} as, for instance, the prompt passed to
> readline when using `read -e -p prompt', those characters need to be there.
>
> --
> ``The lyf so short, the craft so long to lerne.'' - Chaucer
> ``Ars longa, vita brevis'' - Hippocrates
> Chet Ramey, ITS, CWRU c...@case.edu
> http://cnswww.cns.cwru.edu/~chet/
>
>
To follow on to what Greg said:
The only way I've found to output a string containing non-printing sequence
delimiters using the @P transformation is to use read -e -p or to strip the
\[ and \] first. All the other prompt escapes work in printf or echo -e
when using @P.
To reproduce:
red=$(tput setaf 1)
none=$(tput sgr0)
greet='\[$red\]Hello\[$none\]'
printf '%s\n' "${greet@P}"
echo -e "${greet@P}"
read -e -p "${greet@P}"
Naively stripping the delimiters in this case would leave $redHELLO$none
where $redHello is unset or worse.
Granted it makes no sense to have non-printing sequences delimited when
readline isn't involved, but it makes things simpler if you're dealing with
a pre-existing string.
So if @P needs to output \001 and \002 then perhaps there needs to be an @p
which doesn't (unless there's a way to determine whether readline is
involved and only output the delimiters in that case).
--
Visit serverfault.com to get your system administration questions answered.
