Shell 指令詳解之 ​

​if​

​ 指令

1. 常用參數

​

​-eq​

​：等于[equal]

​

​-n​

​ ： 字元串是否不為空

​

​-ne​

​：不等于[not equal]

​

​-le​

​：小于等于[less and equal]

​

​-ge​

​：大于等于[greater and equal]

​

​-lt​

​：小于[less than]

​

​-gt​

​：大于[greater than]

​

​-a​

​： 與 [and]

​

​-o​

​：或 [or]

​

​!​

​：非

• example 1 ​

  ​-eq​

  ​ 腳本如下：

[root@server4 shells]# cat test1.sh 
#!/bin/bash
a=$1
if [ $a -eq 1 ]
then 
 echo a = 1
else
 echo a != 1
fi      

[root@server4 shells]# ./test1.sh 1
a = 1
[root@server4 shells]# ./test1.sh 2
a != 1      

• example 2 ​

  ​-n​

  ​

[root@server4 shells]# cat test1.sh 
#!/bin/bash
a=$1
if [ -n "$a" ];
then 
 echo a isn"'"t empty string
else
 echo a is empty string
fi      

[root@server4 shells]# ./test1.sh 
a is empty string
[root@server4 shells]# ./test1.sh hadoop
a isn't empty string