Re: [Parameter Expansion] bug in ${variable% *}

[Dashing]

On Tue, 12 Feb 2013 18:02:05 +0100 "Chet Ramey"
>I've fixed the problem, and the fix will be in the next release.  

Thank you, Chet!

On Tue, 12 Feb 2013 10:13:46 +0100 "Bernd Eggink"
>superfluous blank in the ${rest: -1} expression

Bernd, this blank makes a big difference:
${rest: -1} last character of $rest
${rest:-1} $rest or 1 if $rest is empty

Re: [Parameter Expansion] bug in ${variable% *}

[Dashing]

On Tue, 12 Feb 2013 14:45:26 +0100 "Greg Wooledge" 
 wrote:
>There are no literal backslashes in an argument that is
>produced by tab completion.  The backslashes are a form
>of quoting, and they are removed by the calling shell
>during the quote removal phase.

When bind -x sets READLINE_LINE backslashes are kept intact. What I 
meant was that I wrote my own tab completion.

>If you believe you have found a bug in parameter expansion,
>then simplify the example so that it directly demonstrates
>the bug.

As I showed in the output, it does not happen all the time. Even 
the same value of $rest one time works and another time does not. 
Therefore, looping over a bunch of items is required.

Re: [Parameter Expansion] bug in ${variable% *}

[Dashing]

On Tue, 12 Feb 2013 14:16:24 +0100 "Greg Wooledge" 
 wrote:
>On Mon, Feb 11, 2013 at 06:50:49PM +0100, Dashing wrote:
>> $ ./pe 'mplayer foo1\ foo2\ foo3\ 4\ 5\ foo6\ 7'
>> :--Mistake--:
>> :--Mistake--:
>
>Whatever you're doing, it's wrong.
>
>./pe mplayer foo1\ foo2\ foo3\ 4\ 5\ foo6\ 7
>
>#!/bin/bash
>prog=$1
>shift
>exec "$prog" extra args go here "$@"
>
>THAT is how a wrapper should be done.  Do not combine a program 
>and its
>arguments all together into a single argument and then try to 
>parse it
>apart.

For my purposes this is irrelevant, because the nature of the 
script from which my example code derived is tab completion. 
READLINE_LINE will contain mplayer foo1\ foo2\ etc. The last 
argument needs to be found and if it contains spaces this is what 
needs to happen.

[Parameter Expansion] bug in ${variable% *}

[Dashing]

Bash version: 4.2.042 

I have a script that behaves erratically:
=
#! /bin/bash
last=${1##* }
rest=${1% *}
while [[ "${rest: -1}" == '\' ]]; do
last="${rest##* } $last"
oldrest=$rest
rest=${rest% *}
if [[ "$oldrest" == "$rest" ]]; then
echo :--Mistake--:
#   sleep 0.01
#   rest=${rest% *}
#   if [[ "$oldrest" == "$rest" ]]; then
#   echo 'unable to interpret'
#   break
#   fi
fi
done
echo REST:$rest:
echo LAST:$last:
=
$ ./pe 'mplayer foo1\ foo2\ foo3\ 4\ 5\ foo6\ 7'
:--Mistake--:
:--Mistake--:
REST:mplayer:
LAST:foo1\ foo1\ foo1\ foo2\ foo3\ 4\ 5\ foo6\ 7:
=

What happens is that rest=${rest% *} doesn't always update $rest, 
even when there are spaces left in $rest.
Meanwhile last="${rest##* } $last" works every time.
In the above example it got stuck twice when $rest was mplayer 
foo1\. It tends to vary wildly.

I have commented out some code including sleep that sometimes helps 
make the parameter expansion work. This commented out code also 
avoids an infinite loop which is triggerable in a normal way with 
an argument of:
command\ filename

Thanks,
Dashing