失败时杀死管道中的下一个命令 [英] Kill next command in pipeline on failure

问题描述

我有一个流式备份脚本，其运行如下:

I have a streaming backup script which I'm running as follows:

./backup_script.sh | aws s3 cp - s3://bucket/path/to/backup

aws 命令以原子方式将stdin流传输到云存储.如果在没有EOF的情况下中断了该过程，则上传将中止.

The aws command streams stdin to cloud storage in an atomic way. If the process is interrupted without an EOF, the upload is aborted.

如果 ./backup_script.sh 以非零退出代码退出，我希望 aws 进程被终止.

I want the aws process to be killed if ./backup_script.sh exits with a non-zero exit code.

是否有执行此操作的bash技巧?

Any bash trick for doing this?

您可以使用以下脚本测试解决方案:

You can test your solution with this script:

#!/usr/bin/env python
import signal
import sys
import functools

def signal_handler(signame, signum, frame):
    print "Got {}".format(signame)
    sys.exit(0)

signal.signal(signal.SIGTERM, functools.partial(signal_handler, 'TERM'))
signal.signal(signal.SIGINT, functools.partial(signal_handler, 'INT'))

for i in sys.stdin:
    pass

print "Got EOF"

示例:

$ grep --bla | ./sigoreof.py
grep: unrecognized option `--bla'
usage: grep [-abcDEFGHhIiJLlmnOoqRSsUVvwxZ] [-A num] [-B num] [-C[num]]
    [-e pattern] [-f file] [--binary-files=value] [--color=when]
    [--context[=num]] [--directories=action] [--label] [--line-buffered]
    [--null] [pattern] [file ...]
Got EOF

我希望 ./sigoreof.py 以信号终止.

推荐答案

使用进程替换而不是命名管道的简短脚本为:

A short script which uses process substitution instead of named pipes would be:

#!/bin/bash

exec 4> >( ./second-process.sh )
./first-process.sh >&4  &
if ! wait $! ; then echo "error in first process" >&2; kill 0; wait; fi

它与fifo的工作原理非常相似，基本上是将fd用作IPC的信息载体，而不是文件名.

It works much like with a fifo, basically using the fd as the information carrier for the IPC instead of a file name.

两句话:我不确定是否需要关闭fd 4；我假设脚本退出后，外壳程序将关闭所有打开的文件.

Two remarks: I wasn't sure whether it's necessary to close fd 4 ; I would assume that upon script exit the shell closes all open files.

我无法弄清楚如何在流程替换中获取流程的PID(有人吗?至少在我的cygwin上，通常的 $！无法正常工作.)因此，我求助于杀死组中的所有进程，这可能不是很理想的(但是我不确定语义).

And I couldn't figure out how to obtain the PID of the process in the process substitution (anybody? at least on my cygwin the usual $! didn't work.) Therefore I resorted to killing all processes in the group, which may not be desirable (but I'm not entirely sure about the semantics).

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