主要是IFS的作用。
/home/lee#a=a
/home/lee#b=b
/home/lee#c="$a $b"
/home/lee#echo $c
a b
/home/lee#oldifs=$IFS
/home/lee#echo $c
a b
/home/lee#IFS=
/home/lee#echo $c
a b
/home/lee#IFS=$oldifs
/home/lee#echo $c
a b
/home/lee#