Re: dash bug: double-quoted "\" breaks glob protection for next char

[Denys Vlasenko <vda.linux@xxxxxxxxxxxxxx>]

On Wed, Feb 14, 2018 at 9:03 PM, Harald van Dijk <harald@xxxxxxxxxxx> wrote:
> Currently:
>
> $ dash -c 'foo=a; echo "<${foo#[a\]]}>"'
> <>
>
> This is what I expect, and also what bash, ksh and posh do.
>
> With your patch:
>
> $ dash -c 'foo=a; echo "<${foo#[a\]]}>"'
> <a>


I was looking into this specific example and I believe it is a _bash_ bug.

The [a\]] is misinterpreted by it (and probably by many people).
The gist is: \] is not a valid escape for ] in set glob expression.
Glob sets have no escaping at all, ] can be in a set
if it is the first char: []abc],
dash can be in a set if it is first or last: [abc-],
[ and \ need no protections at all: [a[b\c] is a valid set of 5 chars.

Therefore, "[a\]]" glob pattern means "a or \, then ]".
Since that does not match "a", the result of ${foo#[a\]]}> should be "a".
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