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Emacs makes assumptions about what constitutes an adequate match for a search. In particular, AFAICT, it disregards whitespace differences, as well as differences in case.

During an incremental search, it is possible to toggle these settings. For example, M-s SPC toggles whitespace matching.

But is there something I can put in my .emacs file such that the default initial settings are the strict ones? (I.e. search for the exact string I have typed in the minibuffer.)

Just to be clear, I still want to be able to toggle these settings. (In fact, my preference would be to selectively adjust these settings for the duration of a search, rather than turning them on or off for the remainder of the session.)

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    C-h k C-s says this: In incremental searches, a space or spaces normally matches any whitespace defined by the variable search-whitespace-regexp; see also the variables isearch-lax-whitespace and isearch-regexp-lax-whitespace. Setting these variables in your .emacs should change defaults. (Whenever I want to customize an Emacs feature, I use C-h k, C-h f, and C-h v to learn more about it. Most of the time it works very well.) – Constantine Feb 6 '16 at 18:51
  • @Constantine: Actually, this suggestion works for whitespace, but not for case-fold, and not just because the documentation for C-s says nothing about it. I find that (1) whereas M-s SPC has a persistent effect on how whitespace is handled in searches, the effect of M-s c lasts only for the duration of the search; and (2) the search is initially case insensitive irrespecitve of the value I assign to the variable isearch-case-fold-search. I've tested this in an Emacs session that I started with emacs -Q -l /dev/null, so I don't think it's due to some weird config. (v24.4.1, Debian) – kjo Feb 6 '16 at 19:25
  • @Constantine: OK, I get it. Even though the variable isearch-case-fold-search does exist, despite its name, it is not really the counterpart of isearch-lax-whitespace with respect to case-fold. That variable is case-fold-search. – kjo Feb 6 '16 at 19:31
  • Do you mind summarizing what worked for you in an answer? (Assuming that you have a solution.) Thanks! – Constantine Feb 6 '16 at 21:08
  • @Constantine: done – kjo Feb 6 '16 at 21:17
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This is what I finally put in my .emacs

(setq isearch-lax-whitespace nil)
(setq isearch-regexp-lax-whitespace nil)

;; the next setting affects both isearch-* and isearch-*-regexp; also, according
;; to its documentation it "[a]utomatically becomes buffer-local when set";
;; therefore, `(setq-default case-fold-search nil)` won't do.
(setq-default case-fold-search nil)

I can still toggle the white-space and case-fold settings during a search, with M-s SPC and M-s c, respectively, but I never figured out how to change either of these settings only for the duration of the search.

Thanks to Constantine for the pointers.

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