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

[tomas]

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.

Cheers
 - t

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