Shell script for adjusting image size

Question

Is there a way to adjust all image sizes in a directory?

If I set the max size to 800x600 it will make larger ones smaller and leave smaller ones at their original size.

Answer 1

for img in *.png; do
    convert "$img" "800x600>" $(basename "$img" .png)_new.png
done

convert is from ImageMagick. ">" says it's only resized if larger. See here for its other options.