bash 关闭缓冲
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Turn off buffering
提问by fodon
Where is the buffer in this following ... and how do I turn it off?
下面的缓冲区在哪里......我该如何关闭它？
I am writing out to stdout in a python program like so:
我在 python 程序中写出标准输出，如下所示：
for line in sys.stdin:
print line
There is some buffering going on here:
这里有一些缓冲：
tail -f data.txt | grep -e APL | python -u Interpret.py
I tried the following to shake off possible buffering ... with no luck:
我尝试了以下方法来摆脱可能的缓冲......但没有运气：
- as above using the -u flag with python invocation
- calling sys.stdout.flush() after each sys.stdout.write() call ... all of these create a buffered stream with python waiting something like a minute to print out the first few lines.
used the following modified command:
stdbuf -o0 tail -f data.txt | stdbuf -o0 -i0 grep -e APL | stdbuf -i0 -o0 python -u Interpret.py
- 如上所述，使用带有 python 调用的 -u 标志
- 在每次 sys.stdout.write() 调用之后调用 sys.stdout.flush() ......所有这些都创建了一个缓冲流，python 等待一分钟来打印出前几行。
使用了以下修改后的命令：
stdbuf -o0 tail -f data.txt | stdbuf -o0 -i0 grep -e APL | stdbuf -i0 -o0 python -u Interpret.py
To benchmark my expectations, I tried:
为了对我的期望进行基准测试，我尝试了：
tail -f data.txt | grep -e APL
This produces a steady flow of lines ... it surely is not as buffered as the python command.
这会产生稳定的线条流......它肯定不像 python 命令那样缓冲。
So, how do I turn off buffering? ANSWER: It turns out there is buffering on both ends of the pipe.
那么，如何关闭缓冲？解答：事实证明，管道的两端都有缓冲。
采纳答案by unutbu
The problem, I believe is in grepbuffering its output. It is doing that when you pipe tail -f | grep ... | some_other_prog. To get grepto flush once per line, use the --line-bufferedoption:
我认为问题在于grep缓冲其输出。当您使用管道时，它就是这样做的tail -f | grep ... | some_other_prog。要grep每行刷新一次，请使用以下--line-buffered选项：
% tail -f data.txt | grep -e APL --line-buffered | test.py
APL
APL
APL
where test.pyis:
在哪里test.py：
import sys
for line in sys.stdin:
print(line)
(Tested on linux, gnome-terminal.)
（在 linux、gnome-terminal 上测试。）
回答by ivan_pozdeev
file.readlines()and for line in filehave internal buffering which is not affected by -uoption (see -u option note). Use
file.readlines()并for line in file具有不受-u选项影响的内部缓冲（请参阅-u 选项注释）。用
while True:
l=sys.stdin.readline()
sys.stdout.write(l)
instead.
反而。
By the way, sys.stdoutis line-buffered by default if it points to terminal and sys.stderris unbuffered (see stdio buffering).
顺便说一下，sys.stdout如果它指向终端并且sys.stderr是无缓冲的，则默认情况下是行缓冲的（请参阅stdio 缓冲）。
回答by Anand Balachandran Pillai
The problem is in your for loop. It will wait for EOF before continuing on. You can fix it with a code like this.
问题出在您的 for 循环中。它将在继续之前等待 EOF。你可以用这样的代码修复它。
while True:
try:
line = sys.stdin.readline()
except KeyboardInterrupt:
break
if not line:
break
print line,
Try this out.
试试这个。
回答by Burhan Khalid
sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)and make sure PYTHONUNBUFFEREDis set in your environment.
sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)并确保PYTHONUNBUFFERED在您的环境中设置。
