Attempting to set non-existent control silently fails

[dtgriscom]

I'm working with a Logitech webcam, and the controls have complex names:

griscom@dell:~$ fswebcam --list-controls
--- Opening /dev/video0...
Trying source module v4l2...
/dev/video0 opened.
No input was specified, using the first.
Available Controls        Current Value   Range
------------------        -------------   -----
Brightness                128 (50%)       0 - 255
Contrast                  32 (12%)        0 - 255
Saturation                32 (12%)        0 - 255
White Balance Temperature, Auto True            True | False
Gain                      45 (17%)        0 - 255
Power Line Frequency      60 Hz           Disabled | 50 Hz | 60 Hz
White Balance Temperature 2800 (0%)       2800 - 6500
Sharpness                 22 (8%)         0 - 255
Backlight Compensation    1               0 - 1
Exposure, Auto            Aperture Priority Mode Manual Mode | Aperture Priority Mode
Exposure (Absolute)       83 (3%)         3 - 2047
Exposure, Auto Priority   True            True | False
Pan (Absolute)            0 (50%)         -36000 - 36000
Tilt (Absolute)           0 (50%)         -36000 - 36000
Focus (absolute)          0 (0%)          0 - 255
Focus, Auto               False           True | False
Zoom, Absolute            1               1 - 5
Adjusting resolution from 384x288 to 352x288.
--- Capturing frame...
Captured frame in 0.00 seconds.
--- Processing captured image...
There are unsaved changes to the image.
griscom@dell:~$ 

A big barrier to figuring this out is that the --set option for fswebcam fails silently if a control isn't known or supported by the camera. Since I didn't know that fswebcam would report each properly set control, and the control effects weren't clear (Logitech's fault, but it made it worse) I was just fishing around with different styled names.

Suggestion: have fswebcam either output a warning, or fail completely, if the user tries to set a control that doesn't exist.

Thanks, Dan

[floretan]

I ran across the same issue, and realized that the control parameters can be used as output with --list-control. It's not pretty, but it works:

fswebcam --set "Zoom, Absolute"=2