All the Special Key Combinations that Change Your Mac's Startup

From http://lifehacker.com/all-the-special-key-combinations-that-change-your-macs-1761327018

• Shift: Starts your Mac in safe mode. This helps you troubleshoot because it only loads the minimum necessary kernel extensions at boot then disables startup items, user-installed fonts, font caches, kernel caches, and other system cache files. Safe mode also runs a file system check automatically, which should help with troubleshooting. 
• Option: This loads up the startup manager where you can pick between different hard drives or discs to boot into. If you need to boot from a hard drive different than your primary one, or you’re booting into Boot Camp, this is the key you push. 
•  C: Boots from a bootable CD, DVD, or USB. This is useful when you’re installing a new operating system. 
• D or Option+D: Starts the Apple Hardware Test on pre-2013 Macs or Apple Diagnostics on newer Macs. Both are meant to help troubleshoot hardware issues. N or 
• Option+N: Starts up from a Netboot server. Most average users will never need to use this as it’s meant for running OS X off a network instead of a hard drive or disc drive. 
• Command+R: Starts up in Recovery mode. If you have problems with your hard drive, OS X Recovery allows you to restore your Mac from a backup, verify and repair your disc, check your internet connection, or reinstall OS X. 
• Command+Option+R: Starts up the internet version of Recovery mode, which works the same as regular Recovery mode, but is online. 
• Command+Option+P+R: This resets the NVRAM. NVRAM stores information about speaker volume, screen resolution, startup disk selection, and recent kernel panic information. If you’re having issues with sound or video, it’s usually a good idea to reset the NVRAM before panicking. 
• Command+S: Starts up in single-user mode. This is meant mostly for developers and IT as a means to troubleshoot startup issues and basically drops you into the command line where you can run tests without worrying about the GUI in OS X. 
•  Command+V: Starts up in verbose mode. Verbose mode is similar to single-user mode but is meant more as a way to watch what a computer is doing to help with troubleshooting. 
• T: Starts your Mac in target disk mode. This is a useful way to share files between two Macs when one of them is broken or the display isn’t working. 
• Eject button, F12, mouse button, or trackpad button: Force eject an optical disk.

Keyboard shortcut to lock macos

⌃ + ⇧ + ⏏ (Control + Shift + Eject)

Here are some useful shortcut keys for the open/save dialog window of macos X:

Spacebar – View the selected item in Quick Look
Command+D – Selects Desktop as the destination
Command+Shift+H – Sets the Home directory as the destination
Command+Shift+A – Sets Applications directory as the destination
Command+Shift+. – Toggle invisible items
Command+Shift+G – Bring up Go To Folder window
Tab – Tab key auto-completes paths and file names from the aforementioned Go To window
Command+R – Open the selected item in the Finder
Command+F – Move the cursor to the Find field
Command+. – Close the Open/Save dialog window

MacOS X Dicionary shortcut

To access the inbuilt MacOS Dictionary you can select a word and press ctrl-cmd-d, you will get the dictionary entry for the selected word. This only works in the more integrated programs: Safari, iWork, etc..

emacs: Cycle windows backward

To cycle windows in emacs you can use the shortcut c-x o that executes the command other-window. Now to cycle windows in the reverse order you need to execute the command other-window with argument -1 (other-window accepts integer as argument, being the number of windows to jump). So I added this code to my .ecmas file:

;; cycle windows in reverse order
(defun prev-window ()
  (interactive)
  (other-window -1)
)
(global-set-key (kbd "C-x p") 'prev-window)

This will create the command prev-window and assign the shortcut C-x p to this function. Note: C-x p is by default assigned to narrow-to-page, a function I never used... This Idea I found it originally in Quora.com

Resize windows in emacs

To easily resize windows in emacs I added the following key shortcuts:

;; * \author Pedro Parracho   
;; Resizing windows using alt-arrow
 (global-set-key (kbd "\033[1;9D") 'shrink-window-horizontally) ;;alt-left: code ^[[1;9D                                                    
 (global-set-key (kbd "\033[1;9C") 'enlarge-window-horizontally) ;; alt-right: code ^[[1;9C                                                 
 (global-set-key (kbd "\033[1;9A") 'shrink-window) ;; alt-up: code ^[[1;9A                                                                  
 (global-set-key (kbd "\033[1;9B") 'enlarge-window) ;; alt-down: code ^[[1;9B                                                               

Now alt-arrow will change the window size by a step.

Swap two characters in emacs

To transpose 2 characters the emacs command is transpose-chars and the shortcut is C-t.
For words the command is transpose-words and the shortcut is M-t.

Go to next unread message in Mail via keyboard

A long standing annoyance in Mail is that there is no keyboard shortcut to skip to the next message. I found in hints.macworld.com a apple script that will jump to the next unread mail on ctr-n.
I changed the script to jump to the last item and not the first, as I like to read my messages by chronological order.

try
 tell application "Mail"
  activate
  tell the front message viewer
   set unreadMessages to (the messages whose ¬
    read status is false) as list
   if (count of unreadMessages) is not 0 then
    set selected messages to {the last item of unreadMessages}
   else
    beep
   end if
  end tell
 end tell
on error error_message
 beep
 display dialog "Error looking for next unread message: " & ¬
  return & return & error_message buttons {"OK"} default button 1
end try

To have this script activated, instead of copying it to the mail script folder as suggested in the article, I created a new service with "no input" in "Mail.app" that will run the apple script on the top. Saved the service, and added the shortcut ctrl-n in the keyboard settings.