Bask 如何判断一个变量是否为空

编写 Shell 脚本时，判断一个变量是否是已经赋值了的。

判断方法

param=
if [ ! -n "$param" ]; then
    echo "is null"
else
    echo "Not is null"
fi

param=
if [ ! $param ]; then
    echo "is null"
else
    echo "Not is null"
fi

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

param=
if [ "$param" = "" ]; then
    echo "is not set!"
else
    echo "is set"
fi

就酱

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