bash 停止 arecord 记录而不停止脚本的其余部分

stopping arecord recording without stopping rest of script

提问by RBI

I am playing with scripts that use the google speech-to-text api. The api requires flac encoded files so the recording part of the script looks like this:

我正在使用使用 google 语音到文本 api 的脚本。api 需要 flac 编码的文件，因此脚本的录制部分如下所示：

arecord -q -t wav -d 0 -f S16_LE -r 16000 | flac - -f --best --sample-rate 16000 -s -o "$TEMP_FILE"

This command will record until the user exits with ctrl-c and the wav recorded format should be piped to the flac program for outut in flac format, then the script should continue.

这个命令会一直录制，直到用户用 ctrl-c 退出，wav 录制的格式应该通过管道传输到 flac 程序以 flac 格式输出，然后脚本应该继续。

The problem I am having is that pressing ctrl-c ends the script entirely and is cutting off some of the audio (the flac file is still outputted). If I run the script without the pipe:

我遇到的问题是按 ctrl-c 会完全结束脚本并切断一些音频（仍输出 flac 文件）。如果我在没有管道的情况下运行脚本：

arecord -q -t wav -d 0 -f S16_LE -r 16000 some.wav

Then pressing ctrl-c will only end the recording and continues on with the script as it should.

然后按 ctrl-c 只会结束录制并继续执行脚本。

How do I fix this so that ctrl-c only stops the arecord command and allows the rest of the script (including the piped flac encoding) to finish?

如何解决此问题，以便 ctrl-c 仅停止 arecord 命令并允许脚本的其余部分（包括管道 flac 编码）完成？

采纳答案by mklement0

Methinks what you're trying to do cannot be done.

我觉得你想做的事是做不到的。

^{Disclaimer: The following is based on my own experiments on Ubuntu 12.04, with just a smattering of research. Do let me know if I'm wrong.}

^{免责声明：以下内容基于我自己在 Ubuntu 12.04 上的实验，仅进行了少量研究。如果我错了，请告诉我。}

The crux:

关键：

• Pressing Ctrl-Cwhile a pipeline is running sends signal SIGINTto ALL processes in the pipeline.
• The orderin which the processes receive the signal is not guaranteed.
• Unless ALL processes in the pipeline trapthe signal, the script will abort as a whole (though the script itself can trap the signal with a trapcommand - but such a shell trap won't execute until afterthe pipeline processes have received the signal and have typically been terminated by it).

• Ctrl-C在管道运行时按下会向管道中的SIGINT所有进程发送信号。
• 不能保证进程接收信号的顺序。
• 除非所有的管道处理陷阱的信号，该脚本将中止作为一个整体（虽然脚本本身可以捕获一个信号trap命令-但这样的罩子套住不会执行，直到后处理已接收到的信号的管道，并有通常被它终止）。

In your specific case, arecordis designedto trapSIGINTand exit in an orderly fashion in response.
By contrast, flacappears not to - it is terminated forcefully.
However, even if flacalso didtrap SIGINTto shut down cleanly, given the nondeterministic order in which the signal is received by the processes involved, you cannot safely use a pipeline with Ctrl-Cwhile expecting overallprocessing to finish in an orderly fashion.

在特定情况下，arecord被设计来捕获SIGINT和退出有序地响应。
相比之下，flac似乎没有 - 它被强行终止。
但是，即使flac也确实使用了陷阱SIGINT来干净地关闭，鉴于所涉及的进程接收信号的顺序不确定，您也不能安全地使用管道，Ctrl-C同时期望整体处理以有序的方式完成。

(As an aside: arecordreports exit code 1when terminated with Ctrl-C, which makes me wonder how you can distinguish that from true failure, such as running out of disk space.)

（顺便arecord说一句：以1终止时报告退出代码Ctrl-C，这让我想知道如何将其与真正的失败区分开来，例如磁盘空间不足。）

Thus:

因此：

• Invoke arecordas a separate commandand capture the output in a (temporary) file.
• Afterward, pass the (temporary) file to flac(and delete the temporary file when done).

• arecord作为单独的命令调用并在（临时）文件中捕获输出。
• 然后，将（临时）文件传递给flac（完成后删除临时文件）。

回答by jmlemetayer

I will try this way:

我会尝试这种方式：

# Create a fifo
FIFO=/tmp/my_fifo
mkfifo $FIFO

# Start arecord in background and redirect its output into the fifo
arecord ... > $FIFO &

# Get the arecord PID
PID=$!

# Trap the SIGINT to send SIGINT to arecord
trap "kill -INT $PID" INT

# Start flac and redirect its input with the fifo.
flac - ... < $FIFO

# The script should be blocked here, and a CTRL+C will run
# the kill -INT to the arecord process only.
# But I don't know how flac will react after ...
# If flac exit correctly, just restore the SIGINT
trap - INT