#! /bin/sh

set dummy 'arg1' 'arg 2' 'arg
3'

echo "1."
for i in "$@"
do
  echo "{$i}"
done

echo "2."
for i in ${1+"$@"}
do
  echo "{$i}"
done

set ${1+"$@"}

echo "3."
for i in "$@"
do
  echo "{$i}"
done