How to detect that a PNG has an alpha channel from command line?

[m^2]

The first thing that I tried was Image Magick. Weirdly, it's 'identify' tool always shows that PNGs are 8-bit ones.
I have a lot of PNGs and want to find the ones with alpha to split the transparency layer out.

[schnaader]

You could give this one a try (from Stack Overflow):

identify -format '%[channels]' foo.png

This should print "rgba" if an alpha channel is present, "rgb" else.

[m^2]

It works, thank you.

[caveman]

pngcheck displays if a picture is in 32-bits or 24-bits mode the same goes for grey+alpha (16-bits) and gray (8-bits, 4 bits, 2-bits and even 1-bit), for instance:
OK: xx.png (210x210, 32-bit RGB+alpha, non-interlaced, 71.9%).
OK: yy.png (559x702, 24-bit RGB, non-interlaced, 38.9%).