1.变量通过“ ”引号引起来

    如下所示,可以得到结果为 is null

    

#!/bin/bash

para1=

if[! -n "$para1"]
then
    echo "is null"

else
    echo "not null"

fi

2.直接通过变量判断:

    如下所示,得到的记过为: is null

#!/bin/bash

para1=

if[!${para1}];then
    echo "is null"
else
    echo "not null"
fi

3.使用test判断

#!/bin/bash


dmin=
if test -z "$dmin"
then
  echo "dmin is not set!"
else  
  echo "dmin is set !"
fi

4.使用""判断

#!/bin/bash
dmin=
if [ "$dmin" = "" ]
then
  echo "dmin is not set!"
else  
  echo "dmin is set !"
fi

参考资料

CSDN

12-09 23:55