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Re: [External] : Re: Regexp for matching control character, say, FORM FE


From: Hongyi Zhao
Subject: Re: [External] : Re: Regexp for matching control character, say, FORM FEED. (Was: Re: The `^L' appeared in built-in help.)
Date: Thu, 22 Jul 2021 09:13:31 +0800

On Thu, Jul 22, 2021 at 1:08 AM Drew Adams <drew.adams@oracle.com> wrote:
>
> > > > M-x insert-char RET form feed (ff) RET
> > >
> > > aka:
> > >
> > > `C-q C-l'
> > >
> > > https://www.gnu.org/software/emacs/manual/html_node/emacs/Inserting-Text.html
> >
> > If I don't know the Unicode name and the above input sequence of it,
> > to be more specifically, I only know its representation in Emacs is
> > ^L, then how to search/match/find/filter out it with regexp.
> >
> > As a similar example, I can grep it with the following
> >
> > $ grep $'\014' 11.txt | cat -te
> > ^L$
> > $ grep $'\f' 11.txt | cat -te
> > ^L$
>
> It's not clear (to me) what you're trying to do.
> The initial question was about _inserting_ the char, I believe.
> For that, `C-q' is the easiest way for a control char, since
> you can just hit the key for the control char (`C-l' in this case).

As I've recapped the title of the issue, I've made another slightly
different discussion from the OP, i.e., searching the document with
regexp for matching the control characters.

> For other Unicode chars, `M-x insert-char' can help, but you don't
> need that just to insert an ASCII control char.
>
> Now you seem to be asking something else, and what it is is not
> clear to me.  If you're asking about search,

Yes, that's what I'm concerned about

> then just use `C-q':
> `C-s C-q C-l'

I want to know whether there are some similar regexp patterns in Emacs
as the ones used by grep, say, $'\014' or $'\f'.

HY



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