[magick-users] how to resize an image based on its alignment (protrate or landscape)?

[kdsfinger at gmail.com]

hi, there
I have a bunch of images mixed with portrate and landscape alignment.
Now I want to resize them so that the maxim side (horizontal for
landscape or vertical for portrate) is set to a fixed number, say,
100. I know geometry or resize can do the job if I know which side is
set to the fixed number. How can I write a bash script to do that?
Thanks for your  help.
zl2k