shift 是將指令列上的參數位置做移動的指令。
ex:
$0= xxx $0= zzz
$1= yyy shift 2 $1= ppp
$2= bbb ======> $2= qqq
$3= ppp $3= null
$4= qqq $4= null
xxx and yyy were shifted out of the order, it'd been thrown away.
ps: Linux 實戰手冊 18-3-3
