Get the content as string of a region in a buffer by elisp program

0
votes

Here is the problem that I'm solving: Convert a region of text into a string data structure for subsequent processing by elisp program. The challenge is that

  1. I want to execute an elisp program interactively without affecting the selection of a region
  2. store the string value into a variable so that I can further manipulate it.

By my understanding, a region is defined by a mark and the subsequent cursor position. And I usually execute elisp program in *scratch* buffer. Furthermore, the region is also in the *scratch* buffer.

But to write the function call and execute it in the buffer, I need to move the cursor away from the end of the text selection (region) in order to write the program of

(setq grabbed (buffer-substring-no-properties (region-beginning) (region-end)))

but then the region of selection would change due to the cursor movement.

So I wonder how I could execute the elisp program while keeping the selection intact and still can access the return value.

2
emacsregion
I think you should rewrite your question in terms of what you want to happen (exact steps the user performs and what you want to happen in response) rather than how you think you need to implement it. As written, I simply don't understand it. - Stefan
Thanks for your feedback! I've simplified my problem statement. - Yu Shen
It's still not clear, to me what you are trying to do. There is no "cursor movement" in the code you show, and it's not clear why the cursor moves "in order to write the program", or even how you are trying to "write the program". Maybe try giving a step-by-step recipe of what you're trying, starting from emacs -Q (no init file), and saying what you see at each step and what you expected to see instead. - Drew

2 Answers

2
votes

If you want to run the function from some Elisp code but as if the user had invoked it via a keybinding, you can use call-interactively:

(setq variable-to-keep-the-value (call-interactively 'lines-to-list))

But in most cases, what you want instead is to take yourself the responsibility to choose to which part of text the function should apply:

(setq variable-to-keep-the-value 
      (lines-to-list (region-beginning) (region-end)))

Notice that the region's boundaries are nothing magical, regardless if they've been set by the mouse or what.

0
votes

Finally, I found a desirable solution! It's using ielm buffer, the real repl of elisp. In the ielm buffer, I can set working buffer (by C-c C-b) to be a buffer where I have the text to be manipulated, for example, *scratch*.

I can then select a region of the working buffer to be processed, and in the ielm buffer then I can type and execute elisp code to extract the text in the selected region in the working buffer, for example,

ELISP> (setq grabbed (buffer-substring-no-properties (region-beginning) (region-end)))
"One\nTwo\nThre"
ELISP> grabbed
"One\nTwo\nThre"
ELISP> (split-string grabbed)
("One" "Two" "Thre")

I can then work with the value held by the set variable, grabbed.

Here is a very helpful description of ielm: https://www.masteringemacs.org/article/evaluating-elisp-emacs