AWK，管道和尾部-f给出了意外的行为 [英] Awk, pipe and tail -f giving unexpected behavior

问题描述

这是我的示例日志文件. http://pastebin.com/DwWeFhJk .

Here is my sample log file.http://pastebin.com/DwWeFhJk.

我在做什么

tail -f log | awk '{if (NF>3) {print $1}; }'

我得到的结果是正确的

64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10
64.242.88.10

但是当我做的时候:

tail -f log |
awk '{if (NF>3) {print $1}; }' |
awk '{print $1}'

我没有得到任何输出.甚至没有输出

I am not getting any output. Even no output in case of

tail -f log | awk '{if (NF>3) {print $1}; }' | grep "64"

我不明白为什么第一个awk的输出没有作为管道后面的第二个awk/grep的输入传递的原因.

I am not getting the reason why the output of the first awk is not getting passed as the input of the second awk/grep after the pipe.

推荐答案

当第一个awk的输出发送到终端时，输出将进行行缓冲，因此每行产生时都会进行打印.当输出进入第二个awk或grep时，它将被完全缓冲.在缓冲区已满之前，将不会发送输出.当足够多的额外记录添加到日志时，第二个awk将缓冲要处理的数据.在那之前，什么都不会发生.

When the output of the first awk is going to the terminal, the output is line-buffered, so each line is printed as it is produced. When the output is going to the second awk or the grep, it is fully buffered. The output won't be sent until the buffer is full. When enough extra records are appended to the log, then the second awk will a buffer full of data to process. Until then, nothing will happen.

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