I've read through
man pngcrush and it seems that there is no way to crush a PNG file and save it over the original. I want to compress several folders worth of PNGs so it would be useful to do it all with one command!
Currently I am doing
pngcrush -q -d tmp *.png then manually cut-pasting the files from the
tmp directory to the original folder. So I guess using
mv might be the best way to go? Any better ideas?