Ctrl-Meta-Space in iTerm2

In Emacs, there’s a handy command called mark-sexp. It marks the rest of the current s-expression from the cursor’s position. It’s mapped to C-M-SPC (ctrl + meta + space) by default, which is compatible with terminal applications.

However, if you have option key mapped to +Esc in iTerm2, pressing ctrl + option + space is interpreted as meta + space instead. To fix this, you need to add an additional keybinding to your session’s key bindings.

1. In iTerm2, open: Preferences > Profiles > some session you wish to edit > Keys.
2. Add a new key binding by pressing the “+” button.
3. Select the “Keyboard Shortcut” field, and press ctrl + option + space.
4. Select “Send Hex Code” in the “Action” list.
5. Type “0x1b 0x00” to the field below the list.
6. Click OK and close the preferences window.

C-M-SPC now works in all the new terminal windows that use the edited session. You can also make the same changes for running terminals by editing the running session.