tar菜单的Bash脚本，case条件中的语法错误

我正在尝试制作一个bash脚本，它响应一个菜单，用户可以从中归档、提取和更新文件。我经常遇到语法错误，但是在我的case条件中，我最近才开始使用bash regex和其他linux工具，所以我在语法上有点混乱，有人能指出在这个例子中，*case结构*中使用条件的正确语法吗？ 以下是我目前掌握的一些代码：

    #!/bin/bash
    echo "Today's date is $(date)"
    echo "The current directory $(pwd)"
    echo -e "A full list of contents follows: $(ls -R)\n"

    echo -e "\n       Archive Menu\n"
    echo "  a.   Archive a file or directory."
    echo "  b.   Extract a file or directory from an archive."
    echo "  c.   Update archive of current directory based on timestamp."
    echo -e "   d.   Exit.\n"
    read -p "Enter a, b, c, or d: " answer
    echo
    #
    case "$answer" in
a)
    read -p "Please enter full path to the file you wish to archive: " path
    read -p "Please enter destination for the archived file (leave empty for current drectory)" dest 
    if [[ "$dest" == null]] ;
        then 
            tar -cvf $path
            tar -tvf $path
            exit 0
        fi;
    if [[ "dest" == ""]];
        then 
            tar -cvf $path $dest
            tar -tvf $path 
            exit 0
        fi;
    ;;
b)
    read -p "Please enter full path to the file you wish to extract: " path 
    read -p "Please enter destination for extracted file (leave empty for current directory)" dest
    if [ "$dest" == null]
        then 
            tar -xvf $path
            tar -tvf $path 
            exit 0
        fi
    if [ "$dest" == ""]
        then
            tar -xvf $path $dest
            tar -tvf $path
            exit 0
        fi
    ;;
c)
   esac

我收到的一些错误消息如下：

   metar.sh:line 18: syntax error in conditional expression: unexpected token';'
   metar.sh:line 18: syntax error near ';'
   metar.sh:line 18 '               if[[ "$dest == null]] ;'

---

在“if”语句的右括号前添加空格，即

if [[ "$x" == "$y" ]]

---

您错过了

]]

前面的空格，它应该是这样的：

if [[ "$dest" == null  ]]
then 
    tar -cvf $path
    tar -tvf $path
    exit 0
fi

或者这个（现在有

然后
和
在同一行，如果
，用
分隔；
）：

您能编辑您的问题以显示您收到的错误消息吗？这将使我们能够准确地指出您的问题，而不必费力地完成整个脚本。
if [[ "$dest" == null  ]] ; then 
    tar -cvf $path
    tar -tvf $path
    exit 0
fi