配管到T型管时强制stdout进行线缓冲 [英] Force line-buffering of stdout when piping to tee

问题描述

通常，stdout是行缓冲的.换句话说，只要您的printf参数以换行符结尾，您就可以期望该行将立即打印出来.使用管道重定向到tee时，似乎不成立.

Usually, stdout is line-buffered. In other words, as long as your printf argument ends with a newline, you can expect the line to be printed instantly. This does not appear to hold when using a pipe to redirect to tee.

我有一个C ++程序a，该程序将始终以\n终止的字符串输出到stdout.

I have a C++ program, a, that outputs strings, always \n-terminated, to stdout.

当它自己运行(./a)时，所有内容都能正确打印并在正确的时间按预期进行打印.但是，如果我将其通过管道传送到tee(./a | tee output.txt)，则在退出之前它不会打印任何内容，这违背了使用tee的目的.

When it is run by itself (./a), everything prints correctly and at the right time, as expected. However, if I pipe it to tee (./a | tee output.txt), it doesn't print anything until it quits, which defeats the purpose of using tee.

我知道我可以通过在C ++程序中的每次打印操作后添加fflush(stdout)来解决此问题.但是，有没有一种更清洁，更轻松的方法?我有没有可以运行的命令，例如，即使使用管道，也可以强制stdout进行行缓冲?

I know that I could fix it by adding a fflush(stdout) after each printing operation in the C++ program. But is there a cleaner, easier way? Is there a command I can run, for example, that would force stdout to be line-buffered, even when using a pipe?

推荐答案

尝试 unbuffer 是 expect 软件包的一部分.您的系统上可能已经有它.

Try unbuffer which is part of the expect package. You may already have it on your system.

在您的情况下，您将像这样使用它:

In your case you would use it like this:

./a | unbuffer -p tee output.txt

(-p用于管道模式，其中unbuffer从stdin读取并将其传递给其余参数中的命令)

(-p is for pipeline mode where unbuffer reads from stdin and passes it to the command in the rest of the arguments)

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