shell判断一个变量是否为空方法总结

shell中如何判断一个变量是否为空的方法探讨，shell编程中，对参数的错误检查项中，包含了变量是否赋值（即一个变量是否为空），判断变量为空方法如下：

1.变量通过” “引号引起来

#!/bin/sh
para1=
if [ ! -n "$para1" ]; then
echo "IS NULL"
else
echo "NOT NULL"
fi
"IS NULL"

2.直接通过变量判断

#!/bin/sh
para1=
if [ ! $para1 ]; then
echo "IS NULL"
else
echo "NOT NULL"
fi
"IS NULL"

3.使用test判断

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

4.使用””判断

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