Your problem isn't with perl, it's with your shell, so you should probably solve it with your shell instead of with perl.

I'm using bash, so I can make it work by escaping the '<' and '>' chars: E.G.
--size=\<45

Or can quote the whole arg, E.G.:
--size="<45"

If you don't want your users to have to deal with that, maybe you'd be better off with different arg names, like:

--min-size=45

or

--max-size=45

Which would be logically equivilent to --size>45 and --size<45 respectively

-Pileofrogs