linux-将块缓冲的数据写入没有fflush(stdout)的文件

据我对缓冲区的了解：缓冲区是临时存储的数据.

例如：假设您要实现一种算法来确定某物是语音还是噪声.您如何使用恒定的声音数据流来做到这一点？这将是非常困难的.因此,通过将其存储到阵列中,您可以对该数据进行分析.

该数据数组称为缓冲区.

现在,我有一个Linux命令,其中的输出是连续的：

stty -F /dev/ttyUSB0 ispeed 4800 && awk -F"," '/SUF/ {print $3,$4,$5,$6,$10,$11,substr($2,1,2),".",substr($2,3,2),".",substr($2,5,2)}' < /dev/ttyUSB0

如果我要将此命令的输出写入文件,将无法写入,因为输出可能是块缓冲的,当我终止上述命令的输出时,只会生成一个空的文本文件( CTRL C).

这就是块缓冲的意思.

The three types of buffering available are unbuffered, block
buffered, and line buffered. When an output stream is unbuffered,
@R_671_4045@ion appears on the destination file or terminal as soon as
written; when it is block buffered many characters are saved up and
written as a block; when it is line buffered characters are saved
up until a newline is output or input is read from any stream
attached to a terminal device (typically stdin). The function
fflush(3) may be used to force the block out early. (See
fclose(3).) normally all files are block buffered. When the first
I/O operation occurs on a file, malloc(3) is called, and a buffer
is obtained. If a stream refers to a terminal (as stdout normally
does) it is line buffered. The standard error stream stderr is
always unbuffered by default.

现在,执行此命令,

stty -F /dev/ttyUSB0 ispeed 4800 && awk -F"," '/SUF/ {print $3,$4,$5,$6,$10,$11,substr($2,1,2),".",substr($2,3,2),".",substr($2,5,2)}' < /dev/ttyUSB0 > outputfile.txt

将生成一个空文件,因为终止进程时缓冲区块可能尚未完成,并且由于我不知道块缓冲区的大小,因此无法等待该块完成.

为了将该命令的输出写入文件,我必须在awk中使用fflush(),它将成功将输出写入文本文件,而我已经成功完成了.

它去了：

stty -F /dev/ttyUSB0 ispeed 4800 && awk -F"," '/GGA/ {print  "Latitude:",$3,$4,"Longitude:",$5,$6,"Altitude:",$10,$11,"Time:",substr($2+50000,1,2),".",substr($2,3,2),".",substr($2,5,2); fflush(stdout) }' < /dev/ttyUSB0 | head -n 2 > GPS_data.txt

但是我的问题是：

有什么方法可以声明缓冲区块的大小,以便我知道何时生成缓冲区块,从而不需要使用fflush()吗？

要么

是否有将缓冲区类型从块缓冲更改为非缓冲或行缓冲的方法？

解决方法:

您可以使用stdbuf运行修改了缓冲区大小的命令.

例如,stdbuf -o 100 awk …将使用100字节标准输出缓冲区运行awk.