Re: [PATCH] expand: Fix naked backslah leakage

On 27/04/2024 13:22, Herbert Xu wrote:
> On Sat, Apr 27, 2024 at 01:12:19PM +0100, Harald van Dijk wrote:
>>
>> The correct result here, I believe, is <\*bc>. The backslash means the next
>> character is taken as literal, even if that character is already also taken
>> as literal because of the quoting. There is nothing to cause the backslash
>> to be taken literally. The result should be that only a leading * is removed
>> from $a.
> 
> While I do see the logic in your reasoning, no other shell implements
> this behaviour:

I'm aware this isn't what most shells do, but it's not quite the case 
that no other shell implements this.

> *sh -c 'a="*bc"; b="\\"; c="*"; echo "<${a##$b"$c"}>"'
> 
> always produces <*bc> across all shells on my system.

This produces <bc> with my shell, at least.

If we are comparing what other shells do, it is probably worth pointing 
out that shells disagree on your original example.

   a="\\*bc"; b="\\"; c="*"; echo "<${a##$b"$c"}>"

Many shells share the bug where this prints <>, but of shells that do 
not have this bug, while many print <bc> like what your patch makes dash 
do, the most commonly used one, bash (as of version 4), does not: it 
prints <\*bc>. I am not sure what exactly $b"$c" is trying to strip here.

Cheers,
Harald van Dijk