如果输入来自文件，那么过滤器管道中的第一个过滤器还具有额外的参数 —— 文件名。
The first filter in a filter pipeline will also have an additional parameter, the filename, if the input comes from a file.
您将注意到这个程序采用两个参数：文件名和客户愿意等待的最长延迟。
You will notice that this program takes two parameters: the filename and the longest delay one is willing to wait.
通常，如果指定了文件名参数，则程序把它作为输入。
Typically, if a filename argument is specified, the program takes that as its input.
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