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shell 练习

2012-11-29 13:29 155 查看

$ {} 注意：

[root@localhost Exercise]# num=2
[root@localhost Exercise]# echo $num
2
[root@localhost Exercise]# echo this is $numnd
this is
[root@localhost Exercise]# echo this is {$num}nd
this is {2}nd
[root@localhost Exercise]# echo this is ${num}nd
this is 2nd
[root@localhost Exercise]#

shell的赋值默认是字符串赋值：

[root@localhost Exercise]# var=1
[root@localhost Exercise]# var=$var+1
[root@localhost Exercise]# echo $var
1+1
[root@localhost Exercise]#

let：

[root@localhost Exercise]# A=1
[root@localhost Exercise]# let A++
[root@localhost Exercise]# echo $A
2
[root@localhost Exercise]# let "A++"
[root@localhost Exercise]# echo $A
3
[root@localhost Exercise]#

$ {}：

[root@localhost Exercise]# echo $A
3
[root@localhost Exercise]# A=$[$A+1]
[root@localhost Exercise]# echo $A
4
[root@localhost Exercise]#

()两个括号：注意！！！

[root@localhost Exercise]# A=1
[root@localhost Exercise]# echo $A
1
[root@localhost Exercise]# A=$(($A+1))
[root@localhost Exercise]# echo $A
2
[root@localhost Exercise]# A=$($A+1)
bash: 2+1: command not found
[root@localhost Exercise]#

[root@localhost Exercise]# echo $(5)
bash: 5: command not found

[root@localhost Exercise]# echo $((5))
5
[root@localhost Exercise]#

[ ] 一个即可：

[root@localhost Exercise]# echo $[5]
5
[root@localhost Exercise]# echo $[[5]]
bash: [5]: syntax error: operand expected (error token is "[5]")
[root@localhost Exercise]#

[ ] 这两个符号的前后都要空格，等号两边不能空格：

#!/bin/bash
#myshell
if [ $SHELL="bin/bash" ];then
echo "your login is $SHELL"
fi

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