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