如果有多個條件

Question

[ -r "$df" ] && { 
     tail -1 $df | grep "$was_fallback" > /dev/null  
     [ $? -ne 0 ] && { continue; }  

這是更大代碼的一部分。我正在閱讀一些由老年人編寫的舊代碼。然後我找到了這段代碼。 我知道[]是'如果'的條件。但是這是用來做什麼的？

Answer 1

I know that [ ] is for 'if' condition 

號這不是如果條件。 [是測試命令。更多關於它在這裏：

What is the difference between test, [ and [[ ?

what is this {} used for? 

這就是所謂的command grouping。從GNU手冊：

{} 

    { list; } 

    Placing a list of commands between curly braces causes the list to be 
    executed in the current shell context. No subshell is created. 
    The semicolon (or newline) following list is required.