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Screencaptures on OSX

Posted on Tue 27 March 2018 in Posts

Oftentimes you want to take a screenshot. On OSX this is easy: ⌘+SHIFT+4 and you're presented with a rectangle that allows you to click & select what to capture. But what happens when you want things like capturing a tooltip, or the mouse pointer itself.

As it turns out there's a command line utility called screencapture that allows you to do this. To capture the screen and include the mouse pointer, you can do:

screencapture -T 5 -C ~/Desktop/screencap.png

and then in 5 seconds the current screen will be saved to ~/Desktop/screencap.png and include the mouse pointer in the image.

But what happens when you have an external display? How do you capture those screens. Well, the answer is in the --help output of the command which reads:

$ screencapture --help
screencapture: illegal option -- -
usage: screencapture [-icMPmwsWxSCUtoa] [files]
  -c         force screen capture to go to the clipboard
  -b         capture Touch Bar - non-interactive modes only
  -C         capture the cursor as well as the screen. only in non-interactive modes
  -d         display errors to the user graphically
  -i         capture screen interactively, by selection or window
               control key - causes screen shot to go to clipboard
               space key   - toggle between mouse selection and
                             window selection modes
               escape key  - cancels interactive screen shot
  -m         only capture the main monitor, undefined if -i is set
  -M         screen capture output will go to a new Mail message
  -o         in window capture mode, do not capture the shadow of the window
  -P         screen capture output will open in Preview
  -I         screen capture output will in a new Messages message
  -s         only allow mouse selection mode
  -S         in window capture mode, capture the screen not the window
  -t<format> image format to create, default is png (other options include pdf, jpg, tiff and other formats)
  -T<seconds> Take the picture after a delay of <seconds>, default is 5
  -w         only allow window selection mode
  -W         start interaction in window selection mode
  -x         do not play sounds
  -a         do not include windows attached to selected windows
  -r         do not add dpi meta data to image
  -l<windowid> capture this windowsid
  -R<x,y,w,h> capture screen rect
  -B<bundleid> screen capture output will open in app with bundleidBS
  files   where to save the screen capture, 1 file per screen

Note that last line, files where to save the screen capture, 1 file per screen. So we just add an additional file per screen. So if you have 2 external displays, you'd do something like:

screencapture -T 5 -C ~/Desktop/screen1.png ~/Desktop/screen2.png ~/Desktop/screen3.png

And three files will be saved, one for each screen.

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