在最后一个示例中，测试home变量的值，用单目操作符- d检查它是不是目录。

In the final example, the value of the HOME variable is tested to see if it is a directory using the -d unary operator.

youdao

生产中应从工艺、设备、操作运转方面改善转杯纱内外在质量，降低单强CV值。

It has to improve the rotor spinning yarn quality from processes, equipment and operation to reduce the single yarn strength CV.

youdao

So this is the equality operator, whereas the single equal sign is the assignment operator.

所以这是相等操作符，然而那个单等号是一个赋值运算符。

哈佛公开课 - 计算机科学课程节选