判斷一個變量是否為空 .

1. 變量通過" "引號引起來

如下所示:，可以得到結果為 IS NULL.

#!/bin/sh

para1=

if [ ! -n "$para1" ]; then

echo "IS NULL"

else

echo "NOT NULL"

fi

2. 直接通過變量判斷

如下所示:得到的結果為: IS NULL

#!/bin/sh

para1=

if [ ! $para1 ]; then

echo "IS NULL"

else

echo "NOT NULL"

fi

3. 使用test判斷

得到的結果就是: 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""判斷

#!/bin/sh

dmin=

if [ "$dmin" = "" ]; then

echo "dmin is not set!"

else

echo "dmin is set !"

fi