Re: Echoing commands in vi visual mode

[Filip Krska]

Hi Chet,

On 06/30/2014 08:55 PM, Chet Ramey wrote:
> On 6/26/14, 4:56 AM, Ondrej Oprala wrote:
> > On 06/11/2014 07:26 PM, Chet Ramey wrote:
> > > On 6/11/14, 6:35 AM, Ondrej Oprala wrote:
> > > > Hi,
> > > > bash-4.3 seems to act differently(better) in vi visual mode, than previous
> > > > bash-4 minors.
> > > > However, ksh gave a different result all along.
> > > This isn't standardized, so I'm not worried about small differences between
> > > implementations in something that happens interactively.
> > True, it's an unimportant detail, though ksh-compliance seems to
> > always be desired.
> Not really.  There's no reason to be deliberately incompatible with other
> shells where non-interactive features are concerned, but ksh is not
> something to be `compliant' with.
Yep, I'd not suggest to take ksh always as an etalon of compliance ;).

However, if we are swimming in "undefined" waters, we can consider 
usability and "user expectation". And in this case, especially when 
substitution occurs in cycle, echoing substituted commands seems not 
only unexpected, but annoying (that's why it was reported to us). See:

If I enter in edit-and-execute-command (C-xC-e) e.g.

for i in $(seq 1 4);do    j=$(echo $i$i );    echo $j; done
echo second

it result for bash-4.3 in:

#
for i in $(seq 1 4);do j=$(echo $i$i ); echo $j; done
seq 1 4
echo $i$i
11
echo $i$i
22
echo $i$i
33
echo $i$i
44
echo second
second

However, with the proposed patch the output reads:

#
for i in $(seq 1 4);do    j=$(echo $i$i );    echo $j; done
11
22
33
44
echo second
second

Of course, treat the patch rather as proof of concept, there may be side 
effect I'm not aware.

> > Anyway, one of my colleagues wrote a small patch that brings
> > the behaviour very close to ksh. Could you please comment on it?
> The interesting thing about this is that very few shells, other than
> bash, seem to inherit the -v option in subshells.  This looks like a
> place where Posix doesn't reflect historical behavior, since Posix says
> that subshell environments inherit all options.  I guess it's a question
> of when the command in the command substitution is `read'.
>
> Chet
Thanks and Regards,

Filip

--
Filip Krška

GSS-SEG EMEA engineer, #sbr-shells (pri), #sbr-anaconda (sec)
Red Hat Czech s.r.o.
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email:fkrska@redhat.com
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