help-gnu-emacs
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Tricky Regexp - How to insert a marker every 3rd number in a sequenc


From: John Mastro
Subject: Re: Tricky Regexp - How to insert a marker every 3rd number in a sequence that begins with a certain delimiter
Date: Sat, 6 Jun 2015 12:08:55 -0700

<gnuist006@gmail.com> wrote:
> tricky regexp
>
> How to insert a marker every 3rd number in a sequence that begins with
> a certain delimiter, and ends with a certain delimiter and its length
> is a multiple of three?
>
> I want to isolate sequences like this in a text and to work on them
> only.
>
> Given:-
>
> text
> text
> BEGIN N N N END
> text BEGIN N N N N N N END
> some text BEGIN N N N N N N N N N END
> text
> N N N N N N N
> text
>
> The sequences I want to work on start with BEGIN and end with END with
> exact multiple of 3 B's in between with only single space. I want to
> place a newline before every 3 B's. So the above text would transform
> to
>
> text
> text
> BEGIN
> N N N
> Z
> text BEGIN
> N N N
> N N N
> Z
> some text BEGIN
> N N N
> N N N
> N N N
> Z
> text
> N N N N N N N
> text

Is there a particular reason you want/need to use a (single) regular
expression? It doesn't seem like a good fit to me. Unless you're
somehow restricted to a single `replace-regexp', you may as well
use more of Emacs's toolbox.

Here's some quick-and-dirty Lisp (which, of course, uses regular
expressions) that works on your example but would need more work and
refinement to serve your general purpose.

    (defun something ()
      (interactive)
      (save-excursion
        (goto-char (point-min))
        (while (re-search-forward "BEGIN" nil t)
          (insert "\n")
          (delete-horizontal-space)
          (while (looking-at "\\(^\\| \\)N N N\\( \\|$\\)")
            (goto-char (match-end 0))
            (delete-horizontal-space t)
            (insert "\n"))
          (when (looking-at "END")
            (replace-match "Z" nil nil nil 0)))))

-- 
john



reply via email to

[Prev in Thread] Current Thread [Next in Thread]