Re: [External] : Use the characters "+" and "-" in regular expressions

[steve-humphreys@gmx.com]

> Sent: Thursday, May 20, 2021 at 10:22 PM
> From: tomas@tuxteam.de
> To: steve-humphreys@gmx.com
> Cc: "help-gnu-emacs@gnu.org" <help-gnu-emacs@gnu.org>
> Subject: Re: [External] :  Use the characters "+" and "-" in regular expressions
>
> On Thu, May 20, 2021 at 12:11:49PM +0200, steve-humphreys@gmx.com wrote:
> >
> >
> > > Sent: Thursday, May 20, 2021 at 9:56 PM
> > > From: tomas@tuxteam.de
> > > To: steve-humphreys@gmx.com
> > > Cc: "help-gnu-emacs@gnu.org" <help-gnu-emacs@gnu.org>
> > > Subject: Re: [External] :  Use the characters "+" and "-" in regular expressions
> > >
> > > On Thu, May 20, 2021 at 11:42:58AM +0200, steve-humphreys@gmx.com wrote:
> > > > I have now used ";; [;+-.]+" to match some specific lines.
> > > >
> > > > (string-match ";; [;+-.]+" s")
> > >                        ^ NOOOO!
> > >
> > > This is a dash in the middle, indicating a range (i.e. "match all
> > > characters in the range "+" to "."). In ASCII (and by extension,
> > > in UTF-8), these are "+", ",", "-" and ".".
> >
> > I thought it was only about numeric and letter ranges only.
>
> No. Any characters can be the endpoints of a range. But this is
> somewhat dangerous, since, strictly speaking, the results might
> depend on the character encoding. Nowadays, with ubiquitous Unicode,
> this is less of a problem. In the context of Emacs, which probably
> always uses its internal set (a superset of Unicode), results are
> probably always consistent.
>
> That doesn't mean they are always intuitive. Quick: is "d" in
> the range "[(-{]"?
>
> Don't do that. Your reader will thank you.
>
> Again: please, play with it. Make yourself test cases.

Done some tests and got some strange results that thought would not match.  Then things
made more sense after your clarification because when I looked at some of the strings,
there was a comma in them.

Am seeing how to match strings of blank lines

But " +" does not do the job.  I know why, but how can one match strings of blanks?


> Cheers
>  - t
>