/tmp{a,b} = /tmp/a, /tmp/b
/tmp/{tom,jerry}/hi = /tmp/tom/hi,/tmp/jerrry/hi
//如何创建/tmp/x/y1,/tmp/x/y2,/tmp/x/y1/a,/tmp/x/y2/a,/tmp/x/y2/b
mkdir /tmp/x/{y1,y2}/{a,b}
//如何创建x_m,y_m,x_n,y_n
mkdir {x,y}_{m,n}
原文：http://11077520.blog.51cto.com/11067520/1964445