Emacs remember text selection

Question

Hello all. I decided that I was ready to try something new, after a few years of using gEdit for most of my coding needs, and try to learn using Emacs. I knew this would be difficult, as I have heard how complex Emacs can be, but I was lured by its power. The hardest thing has been getting used to writing ELisp in the .emacs file to change things about the editor. I can't currently do it myself, but I have found a few helpful snippets here and there to change some options.

One thing I have been having a lot of problems with is getting Emacs to remember the text I have selected after a command. For instance, I commonly highlight a section of code to mass indent it. However, if I do this in Emacs, it will move the selected text only once before unselecting all of the text. Does anyone know a way around this?

Anyway, I apologize for what seems to me to be an easy question, but after an hour of Google searching and looking around here on SO, I thought it was worth asking. I have a few more questions about Emacs, but I will save them and ask separately after I get this straightened out. Thanks!

UPDATE

A few people have asked about what mod I am using and what type of text I am entering. While I don't know much about Emacs modes, I am editing a pure text file at the moment. Something like this:

Hello, I am a simple text file
that is made up of three separate 
lines.

If I highlight all three lines and hit TAB, I get this:

    Hello, I am a simple text file
    that is made up of three separate 
    lines.

This is great, however, if I use C-x C-x like some suggest below to reselect the text and hit TAB again, I get this:

        Hello, I am a simple text file
            that is made up of three separate 
                lines.

I hope this helps!

Answer 1

How are you indenting, and in which mode?

The indentation rules in any programming mode should generally just get it right. (If they don't, that's probably more indicative that you want to configure the rules for that mode differently, but I suspect that's a different question which has been asked already).

If you're in text-mode or similar and just using TAB, then I can see the problem.

Note that if you're using indent-rigidly (C-x C-i, or C-x TAB which is the same thing) then you can repeatedly indent the same region simply by repeating the command, even if the highlighting has disappeared from view.

You can also use a prefix arg to indent-rigidly to make it indent many times. e.g. C-u C-u C-x C-i (easier to type than it looks) will indent 16 spaces (4 x 4, as the prefix arg defaults to 4, and it multiplies on each repeat). Similarly, M-8 C-x C-i indents 8 spaces. This is fine in some circumstances, and way too cumbersome in others.

Personally I suggest putting (cua-selection-mode 1) into your .emacs and using that for rigid indentation. Trey Jackson made a handy blog about it. With this, you can C-RET to start rectangle selection, down as many lines as you need, TAB repeatedly to indent the lines, and C-RET to exit the mode.

While the rectangle is active, RET cycles through the corners. For left-hand corners, typing inserts in front. For right-hand corners, typing inserts after. For the single-column rectangle, bottom counts as 'left' and top counts as 'right' for this purpose.

Trey's blog lists all the available features (or look in the source file: cua-base.el)

Be warned that indentation in Emacs is generally an unexpectedly complicated topic.

Answer 2

Try typing C-x C-x after Emacs unselects it.

Then, instead of hitting tab (I never knew that tab does what you said! That's totally whacked.), do M-8 C-x C-i. Pity it's so many keys, but it ought to do what you want -- namely, shove everything over 8 columns. Obviously replace the M-8 with something else if you want some other number of columns.

Answer 3

What I usually do is simply type C-x C-x (exchange-point-and-mark) after a command that deactives the region.

Answer 4

FWIW, here is the reason for the behaviour of your newly-added example. (I'm not 'solving' the issue here, but I'm posting it to demystify what you're seeing.)

This was determined with emacs -q which disables my customisations, so the following is default behaviour for emacs 23.2.

1. You are in text-mode. You should see (Text) or similar in the mode line at the bottom of the screen, and C-h m will tell you (under the list of minor modes) "Text mode: Major mode for editing text written for humans to read." Emacs decides (by way of the auto-mode-alist variable) that it should switch to text-mode if you visit a filename matching certain extensions (such as .txt).

2. In text-mode pressing TAB with a region highlighted causes indent-according-to-mode to be called on each line of the region in sequence. The slightly convoluted path to finding this out starts at C-h k TAB, which tells us that TAB is bound to indent-for-tab-command, which in this instance calls indent-region -- that function name is not stated explicitly in the help, but can be seen in the code -- which checks the buffer-local indent-region-function variable, which is nil, and: "A value of nil means really run indent-according-to-mode on each line."

3. indent-according-to-mode checks the indent-line-function variable, which has the buffer-local value indent-relative.

4. Use C-h f indent-relative RET to see the help for this function. (Read this).

Although you probably won't yet have had the experience to know how to check all that (or necessarily even want to!), and fully understand everything it tells you, this is an example of how the self-documenting aspect of Emacs enables a user to figure out what is going on (which then makes it feasible to change things). I essentially just used C-h k (describe-key), C-h f (describe-function), and C-h v (describe-variable) to follow the documentation. Looking at the source code for indent-for-tab-command was as simple as clicking the file name shown as part of its help page.

I suggest doing the following to help see what is happening when indent-relative runs on each line:

M-x set-variable x-stretch-cursor t
M-x set-variable ruler-mode-show-tab-stops t
M-x ruler-mode

Now for each line in turn, put the cursor at the very start of the line and press TAB. You'll end up with all three lines indented to the first tab-stop ('T' in the ruler).

Now repeat this -- again, ensure you are at the very start of each line, in front of the existing indentation.

The first character of the first line (which is currently a tab) is once again indented to the first tab-stop, as there is no preceding line for it to examine.

Next, the first character of the second line is indented to match the position of the first non-white-space character of the preceding line. Because the first character of the second line is also a tab, the actual text of the second line is pushed one tab further along.

The third line follows suit. Its first tab character is lined up with the first non-white-space character of the second line, with the same relative effect as before, giving you the final state in your example.

To emphasise, note what happens if you now put enter the line "a b c" above the existing lines, then move back to the start of the next line (what was previously the first line) and press TAB. The first tab character will now be indented in line with the 'b'. Provided that the indent-tabs-mode variable is true (meaning you have actual tab characters), then this will have no practical effect on the position of the words in the line, as 'indenting' a tab with spaces will not have an effect until the number of spaces exceeds the width of the tab (but that's another kettle of fish entirely!)

All this really means is that text-mode in Emacs doesn't behave the way you'd like it to in this situation. Other major modes can do completely different things when you press TAB, of course.

As is invariably the case with Emacs, things you don't like can be changed or circumvented with elisp. Some searching (especially at the Emacs Wiki) will frequently turn up useful solutions to problems you encounter.

Answer 5

You can do this with something like the following:

(add-hook 'text-mode-hook (lambda ()
                            (set (make-local-variable 'indent-region-function)
                                 (lambda (s e)
                                   (indent-rigidly s e tab-width)))))

Then selecting a region and hitting TAB. will indent the region by a tab-width. You can then exchange point and mark with C-x C-x and hit TAB again to repeat.

I do, however, agree with the previous answers that suggest using indent-rigidly directly.