shell判断一个变量是否为空

判断一个变量是否为空 .

1. 变量通过" "引号引起来

如下所示:，可以得到结果为 IS NULL.

        #!/bin/sh

        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:得到的结果为: IS NULL

        #!/bin/sh

        para1=

        if [ ! $para1 ]; then

            echo "IS NULL"

        else

            echo "NOT NULL"

        fi

         

3. 使用test判断

     得到的结果就是: dmin is not set!

        #!/bin/sh

        dmin=

        if  test -z "$dmin"  then

          echo "dmin is not set!"

        else 

          echo "dmin is set !"

        fi

 

 

4. 使用""判断

        #!/bin/sh 

        dmin=

        if [ "$dmin" = "" ]; then

          echo "dmin is not set!"

        else 

          echo "dmin is set !"

        fi