How can I repeatedly take a screenshot of a specific area in OS X?

Question

Under OS X, I need to take a screenshot of the same specific screen area. I know I can press hotkeys to grab the entire screen, or an area of the screen, but then I always have to select it.

Can I configure OS X to always create a screenshot of the same part of the screen?

Answer 1

You can use the screencapture command line utility. It includes (amongst others) the following options:

-x         do not play sounds
-R<x,y,w,h> capture screen rect
files   where to save the screen capture, 1 file per screen

So, in your case, to grab a screenshot with the top left corner at 20/20, creating a 640x380 window:

screencapture -x -R20,20,640,380 ~/Desktop/test.png

You could put this command into your crontab to have it execute repeatedly, or simply use a loop that runs in a Terminal window. In that case, we will create a screenshot every second (sleep 1), and the output file will be named screen_YYMMDDTHHMMSS accordingly.

while [ 1 ]; do 
  date=$(date "+%Y%m%dT%H%M%S")
  screencapture -x -R20,20,640,380 ~/Desktop/"screen_${date}.png"
  sleep 1
done

You could also create an Automator action or AppleScript to run a shell script like the above. For example, open Script Editor, then paste this:

do shell script "date=$(date '+%Y%m%dT%H%M%S'); screencapture -x -R20,20,640,380 ~/Desktop/screen_${date}.png"

It should look like this:

Save that script and use FastScripts to easily assign a keyboard shortcut.

Answer 2

If you are open to using an app/utility, I would highly recommend Skitch:

https://evernote.com/skitch/

It has a shortcut for "Previous Snapshot Area."

(In addition you can capture a selection using a timer, capture the whole screen, just a window, or just a menu.)

It's free and has a ton of features including editing / annotations, quick and easy sharing, etc.

Answer 3

Not sure if this was introduced in newer macOS versions, but now one can just use cmd + shift + 5, select desired area and choose "Capture Selected Portion" from the toolbar below. After selecting area once, it stays exactly the same on the following screen capture calls.

Answer 4

^{Copied from my own answer at Ask Different}
You can now do this natively, Apple added to the previous capture commands of Cmd ⌘ Shift ⇧ 3 and Cmd ⌘ Shift ⇧ 4 by adding Cmd ⌘ Shift ⇧ 5 [This functionality was added in Mojave.]

This exposes all the preferences for the Screenshot process right there on screen. If you select a specific area, then it will return to this same area [& selected Preferences in the Options button] every time you trigger it, until you change it. You take the shot with the Capture button, or Return/Enter key. It will otherwise wait for you. You can also add a timer, change location, etc that you previously had to access from terminal.

^{I've manipulated the window position in this capture so you can see both in the same shot.
BTW, you can screenshot the screenshot mechanism using Cmd/Shift/3}