learning uboot test command

uboot commad test

　　test - minimal test like /bin/sh

　　so we can use test command to some judge

　　for example,

　　　　test –n $uenvcmd    test var uenvcmd length ！eq  zero

　　　detail learning you  can reference url: https://www.cnblogs.com/tankblog/p/6160808.html

　

　Note: we can use test command to make dual system design　　

　　　　you can reference url : https://www.cnblogs.com/lianghong881018/p/9580236.html