Screencapture -l : illegal option?

问题

I've seen in many pages here on SO (for example here: https://apple.stackexchange.com/questions/56561/how-do-i-find-the-windowid-to-pass-to-screencapture-l) that you have to use the command: screencapture -l in order to capture a single window given its ID.

However when I try to enter screencapture -l into the terminal I get this error:

screencapture: illegal option -- l

I've checked a reference and actually I can't see -l as a possible attribute for screencapture: http://guides.macrumors.com/screencapture

How do you explain this? How can I solve this?

回答1:

Not certain if this is a programming question or something better suited for apple.stackexchange.com, but anyways:

When I run "screencapture -l", I see this:

screencapture: illegal option -- l
usage: screencapture [-icMPmwsWxSCUtoa] [files]
  -c         force screen capture to go to the clipboard
  -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
  -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
  files   where to save the screen capture, 1 file per screen

They don't make it clear in the above output ("windowsid"?), but it looks like the "-l" option requires a window id, so that screencapture would capture a single window on the screen.

来源：https://stackoverflow.com/questions/18667214/screencapture-l-illegal-option