Is there a built-in way to both save and copy a screenshot to the clipboard at the same time?
Solution 1:
According to man screencapture one can only save to the clipboard or to a file: there doesn't seem to be any way around this as designed.
The description of the command uses the word 'or' to indicate that only one action is possible: save the screencapture to a file or to the clipboard:
Solution 2:
Check out this question: What's the quickest way to get a graphic on the clipboard saved to disk?
And this utility:
pngpaste
Paste PNG into files, much like pbpaste does for text.