shift左移命令

shift命令把所有参数变量左移一个位置，使$2变成$1,$3变成$2，依此类推。原来$1的值将被丢弃，而$0仍将保持不变。如果调用shift命令时指定了一个数值参数，则表示所有的参数将左移指定的次数。

   在扫描处理脚本程序的参数时，经常要用到的shift命令，如果你的脚本需要10个或10个以上的参数，你就需要用shift命令来访问第10个及其后面的参数。

    例子如下：

#!/bin/bash
 my_fun()
 {
   echo '$0 inside function is '$0
   echo '$1 inside function is '$1
   echo '$2 inside function is '$2
 }

 echo '$0 outside function is '$0
 echo '$1 outside function is '$1
 echo '$2 outside function is '$2
 echo '$3 outside function is '$3
 echo '$4 outside function is '$4
 echo '$5 outside function is '$5
 echo '$6 outside function is '$6
 echo '$7 outside function is '$7
 echo '$8 outside function is '$8
 echo '$9 outside function is '$9
 shift 9
printf "\n"
echo '$0 outside functionaaaaaaaaaaaaaaaaaa is '$0
 echo '$1 outside bbbbbbbbbbbb function is '$1
 echo '$2 outside bbbbbbbbbbbb function is '$2

echo '$3 outside bbbbbbbbbbbb function is '${3}aaaaaaaaaaa
 echo '$4 outside bbbbbbbbbbbb function is '$4
printf "\n"
echo '$10 outside function is '${10}
 echo '$11 outside function is '$11
 echo '$12outside function is '$12
 printf "\n"
 my_fun fp1 "fp2 fp3"

运行：

# ./shift1 one two three four five six seven eight nine ten eleven twelve
输出结果：

$0 outside function is ./shift1
$1 outside function is one
$2 outside function is two
$3 outside function is three
$4 outside function is four
$5 outside function is five
$6 outside function is six
$7 outside function is seven
$8 outside function is eight
$9 outside function is nine

$0 outside functionaaaaaaaaaaaaaaaaaa is ./shift1
$1 outside bbbbbbbbbbbb function is ten
$2 outside bbbbbbbbbbbb function is eleven
$3 outside bbbbbbbbbbbb function is twelveaaaaaaaaaaa
$4 outside bbbbbbbbbbbb function is

$10 outside function is
$11 outside function is ten1
$12outside function is ten2

$0 inside function is ./shift1
$1 inside function is fp1
$2 inside function is fp2 fp3
~#

 

注意要分清楚:
$10 就是 ${1}0 不是 ${10}