The purpose of this question is primarily to serve my curiosity, but it can maybe save some time for others who may press C-M-s (isearch-forward-regexp) just like they would press C-s (isearch-forward), but who would see nothing happening.

In fact, when I press C-M-s just like I would for any other keystroke, nothing happens, and I lately figured out I had to hold it pressed for about half a second for it to work.

This is also the case if I want to get the description of C-M-s using C-h k.

What is the reason for that? Is it related to my configuration?

  • To test whether it is related to your configuration, try starting emacs as emacs -Q under both terminal and graphical environments. I guess the keys could conceivably be intercepted by the terminal emulator or window manager. – Basil May 29 '17 at 11:05
  • @Basil Did you mean "emacs -q" ? – Giuseppe May 29 '17 at 11:46
  • No, but you can try that too; -Q implies -q in addition to disabling other custom initialisation code that may be installed on your system. See here for more information. – Basil May 29 '17 at 11:58
  • After trying starting Emacs that way (both with and without GUI), the result is the same. Only with the -Q option the GUI window is minimized when I press C-M-s. – Giuseppe May 29 '17 at 12:20

This was apparently due to Ubuntu (with Unity): C-M-s was in my case a default key-binding for minimizing windows.

Hence a conflict, I guess. Redefining it to something else solved the problem.


C-h f isearch-forward-regexp, then you will find:

C-M-s (translated from C-M-S-s) runs the command

C-M-S-s works(GNU Emacs 25.1.1) for me.

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