仅当重定向到管道或文件时，awk才会输出 [英] No output from awk only when redirected to pipe or file

问题描述

我有一个相当简单的脚本(在向每行添加时间戳后，从tty打印内容).它可以在命令行上很好地输出，但是用>重定向输出不起作用.为什么不呢?

I have a rather simple script (print content from a tty after adding timestamp to every row). It outputs nicely on the command line, but redirecting the output with > does not work. Why not?

这是脚本:

#!/bin/bash
awk '{ print strftime("%Y-%m-%d %H:%M:%S |"), $0; }' "$1"

按原样运行它，就像timecat /dev/ttyACM0正常工作一样，我在终端中看到了内容.

Running it as is, like timecat /dev/ttyACM0 works fine, I see the content in my terminal.

但是，如果我运行timecat /dev/ttyACM0 > ~/tmp.log，则什么也不会出现.与tee相同.该文件在那里，但为空.

But if I run timecat /dev/ttyACM0 > ~/tmp.log, nothing comes out. Same with tee. The file is there, but it is empty.

脚本中的awk是否有些怪异，如何修改它以使重定向有效?

Is there something weird with awk in the script, how can I modify this to make the redirection work?

推荐答案

所需要做的就是刷新命令中的打印内容，并用以下命令替换最后一个脚本行:

All this needed was to flush the print within the command, replacing the last script row with this:

awk '{ print strftime("%Y-%m-%d %H:%M:%S |"), $0; fflush(); }' $tty
                                                  ^^^^^^^^^

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