Re: bash core dumps doing glob pattern on long string

[Dennis Williamson]

On Tue, Oct 11, 2022, 3:12 PM Greg Wooledge <greg@wooledge.org> wrote:

> On Tue, Oct 11, 2022 at 12:38:44PM -0700, Koichi Murase wrote:
> > As far as I know, glob/extglob
> > does not have constructs that cannot be represented by formal regular
> > languages so should always be able to be represented by NFAs and thus
> DFAs.
>
> It's been too many decades since I studied this stuff in college, but
> earlier while reading the thread I was pondering converting extglobs
> into (ERE) regular expressions.
>
> Extglobs add 5 features:
>
>               ?(pattern-list)
>                      Matches zero or one occurrence of the given patterns
>               *(pattern-list)
>                      Matches zero or more occurrences of the given patterns
>               +(pattern-list)
>                      Matches one or more occurrences of the given patterns
>               @(pattern-list)
>                      Matches one of the given patterns
>               !(pattern-list)
>                      Matches anything except one of the given patterns
>
> The first 4 can be converted directly into ERE without any issues at all.
> The last one cannot.  At least not easily.
>
> The part I can't remember is whether !(foo) can be expressed in a regular
> language.  My gut says "no", but there might be some trick that I've
> forgotten.  A regular language has concatenation (abc), union (abc|def),
> and close (a*bc*) but not negation.
>


Can't you just match and negate?

>