if a clothing dryer is located outside, you don't need an exhaust hose?

not at all ,,,,,,,,,,,,,,,,,

You need to vent exhaust away from the dryer or your intake will be sucking in exhaust heavy with humidity.  That means much longer drying time.

I would say, No, you don't NEED a dryer exhaust on in an outdoor installation. 

Howsoever, you say the dryer is located next to a wall. Know that without a proper exhaust hose, moisture will likely accumulate behind the dryer as will a bunch of dryer lint for you to clean.

correct you don't 

No vent required.  

Check the building codes on your area.

Yes, you still need an exhaust hose because the lint will build up by the dryer if you don't, and it's an EXTREME fire hazard if it does. 

Personally I'd want to get all that moisture away from directly behind the machine.  I'd worry about premature rusting.  It costs less than ten bucks for a hose.

Not necessary for the proper operation of the dryer - - - but consider that even with 18 inches clearances from the wall, you are venting a lot of moisture and lint against it.

That is correct...