if语句根据bash中的变量给出不同的错误

Question

我有一些bash代码（抱歉格式化，Stack Overflow不起作用）：

read -p "Start server and create configuration files (y or n)?  : " startserver
if [ $startserver = "y" ]
        then java -Xmx1024M -jar craftbukkit.jar -o true
elif [ $startserver = "n" ]
        then exit 0
        else invalid;
fi

它生成应该说“无效！”当我输入y或n以外的东西时。当输入中没有空格时，它会这样做。如果我输入一个空格，我会收到以下错误：

/home/snuggles08/Documents/CraftBukkit Installer.sh: line 5: [: =: unary operator expected
/home/snuggles08/Documents/CraftBukkit Installer.sh: line 7: [: =: unary operator expected

当文本有空格时，我收到以下错误：

/home/snuggles08/Documents/CraftBukkit Installer.sh: line 5: [: too many arguments
/home/snuggles08/Documents/CraftBukkit Installer.sh: line 7: [: too many arguments

为什么会这样？