从文件中读取，或标准输入 [英] Read from File, or STDIN

问题描述

我编写了一个命令行实用程序，它使用 getopt 来解析命令行上给出的参数.我还希望文件名是一个可选参数，例如它在 grep、cut 等其他实用程序中.所以，我希望它具有以下用法

I've written a command line utility that uses getopt for parsing arguments given on the command line. I would also like to have a filename be an optional argument, such as it is in other utilities like grep, cut etc. So, I would like it to have the following usage

tool -d character -f integer [filename]

如何实现以下内容?

• 如果给出了文件名，则从文件中读取.
• 如果没有给出文件名，则从 STDIN 读取.

推荐答案

简单来说:

import sys
# parse command line
if file_name_given:
    inf = open(file_name_given)
else:
    inf = sys.stdin

此时您将使用 inf 从文件中读取.根据是否给定文件名，这将从给定的文件或标准输入读取.

At this point you would use inf to read from the file. Depending on whether a filename was given, this would read from the given file or from stdin.

当你需要关闭文件时，你可以这样做:

When you need to close the file, you can do this:

if inf is not sys.stdin:
    inf.close()

然而，在大多数情况下，如果你完成了关闭 sys.stdin 是无害的.

However, in most cases it will be harmless to close sys.stdin if you're done with it.

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