如果有多个条件

Question

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

这是更大代码的一部分。我正在阅读一些由老年人编写的旧代码。然后我找到了这段代码。 我知道[]是'如果'的条件。但是这是用来做什么的？

Answer 1

I know that [ ] is for 'if' condition 

号这不是如果条件。 [是测试命令。更多关于它在这里：

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

what is this {} used for? 

这就是所谓的command grouping。从GNU手册：

{} 

    { 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.