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并行运行 if 条件

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并行运行 if 条件

我有一个像这样的脚本：

#!/bin/bash

if findmnt --source UUID=309689b5-ea5c-4175-84c7-192631553eab --source PARTLABEL=WDPurple8TB --mountpoint /media/ismail/WDPurple8TB --types ext4 --noheadings; then
    udisksctl unmount -b /dev/disk/by-label/WDPurple8TB
    udisksctl power-off -b /dev/disk/by-label/WDPurple8TB
    echo "Power-Off /dev/disk/by-label/WDPurple8TB"
fi

if findmnt --source UUID=151cf7f0-461a-416f-8e44-63d799418958 --source PARTLABEL=WDPurple6TB --mountpoint /media/ismail/WDPurple6TB --types ext4 --noheadings; then
    udisksctl unmount -b /dev/disk/by-label/WDPurple6TB
    udisksctl power-off -b /dev/disk/by-label/WDPurple6TB
    echo "Power-Off /dev/disk/by-label/WDPurple6TB"
fi

在这里，如果两个 if-fi 代码块并行运行会更好。但是，if-fi 代码块中的 stdout 和 stderr 应该成组（我的意思是它们的输出不应重叠）。我的意思是：

以下三行的 stdout 和 stderr 应在我们到达末尾后显示第一的if-fi 代码块。

udisksctl unmount -b /dev/disk/by-label/WDPurple8TB
udisksctl power-off -b /dev/disk/by-label/WDPurple8TB
echo "Power-Off /dev/disk/by-label/WDPurple8TB"

以下三行的 stdout 和 stderr 应在我们到达末尾后显示第二if-fi 代码块。

udisksctl unmount -b /dev/disk/by-label/WDPurple6TB
udisksctl power-off -b /dev/disk/by-label/WDPurple6TB
echo "Power-Off /dev/disk/by-label/WDPurple6TB"

我怎样才能做到这一点？

答案1

要序列化这些输出（和错误），您必须暂时保存至少其中一个：

#! /bin/zsh -
ret=0
umask 077 # for temp files that we recreate
if findmnt --source UUID=309689b5-ea5c-4175-84c7-192631553eab --source PARTLABEL=WDPurple8TB --mountpoint /media/ismail/WDPurple8TB --types ext4 --noheadings; then
    udisksctl unmount -b /dev/disk/by-label/WDPurple8TB &&
      udisksctl power-off -b /dev/disk/by-label/WDPurple8TB &&
      echo "Power-Off /dev/disk/by-label/WDPurple8TB"
fi & pid=$!

out==() err==()
if findmnt --source UUID=151cf7f0-461a-416f-8e44-63d799418958 --source PARTLABEL=WDPurple6TB --mountpoint /media/ismail/WDPurple6TB --types ext4 --noheadings; then
    udisksctl unmount -b /dev/disk/by-label/WDPurple6TB &&
      udisksctl power-off -b /dev/disk/by-label/WDPurple6TB &&
      echo "Power-Off /dev/disk/by-label/WDPurple6TB"
fi > $out 2> $err || ret=$?

wait $pid || ret=$?

# dump the second job's errors on stderr
cat<$err >&2

# and its output to stdout:
cat<$out

# clean up the temp files
rm -f -- $out $err

# report failure if any of any of those two jobs
exit $ret

这里使用进程替换zsh的=(...)形式来创建临时文件。通过 sh 或 bash，您可以使用mktemp系统上可用的任何命令来安全地创建临时文件。

严格来说，=(cmd)并不是这样使用的，因为一旦扩展的命令完成，zsh 就会删除临时文件。在这里，我们稍后使用相同的路径重新创建它，因此它并不严格安全，因为有一个小窗口，在此期间文件可能被恶意行为者重新创建为符号链接。

对于任意数量的并行卸载，我们可以稍微分解一些事情。我们还可以打开 fds 到那些要删除的临时文件，以便从一开始就删除它们，解决上述问题并进行清理：

#! /bin/zsh -
zmodload zsh/system || exit
out=() err_read=() err_write=() out_read=() out_write=() pid=()
n=1 ret=0

stop_disk() {
  local uuid=$1 label=$2
  if
    findmnt --source UUID=$uuid \
            --source PARTLABEL=$label \
            --mountpoint /media/ismail/$label \
            --types ext4 \
            --noheadings
  then
    udisksctl unmount -b /dev/disk/by-label/$label &&
      udisksctl power-off -b /dev/disk/by-label/$label &&
      print -r "Power-Off /dev/disk/by-label/$label"
  fi
}

for uuid label (
  309689b5-ea5c-4175-84c7-192631553eab WDPurple8TB
  151cf7f0-461a-416f-8e44-63d799418958 WDPurple6TB
) {
  () {
     sysopen -wo cloexec -u out -- $1 &&
       sysopen -ro cloexec -u in -- $1 &&
       err_write[n]=$out err_read[n]=$in &&
       sysopen -wo cloexec -u out -- $2 &&
       sysopen -ro cloexec -u in -- $2 &&
       out_write[n]=$out out_read[n]=$in
  } =() =() || exit

  stop_disk $uuid $label >&$out_write[n] 2>&$err_write[n] &
  pid[n++]=$!
}

for (( i = 1; i <= n; i++ )) {
  wait $pid[i] || ret=$?
  cat <&$err_read[i] >&2
  cat <&$out_read[i]
}

exit $ret

（未经测试）

答案2

这行得通吗：

#!/bin/bash

a() {
    if findmnt --source UUID=309689b5-ea5c-4175-84c7-192631553eab --source PARTLABEL=WDPurple8TB --mountpoint /media/ismail/WDPurple8TB --types ext4 --noheadings; then
        udisksctl unmount -b /dev/disk/by-label/WDPurple8TB
        udisksctl power-off -b /dev/disk/by-label/WDPurple8TB
        echo "Power-Off /dev/disk/by-label/WDPurple8TB"
    fi
}
b() {
    if findmnt --source UUID=151cf7f0-461a-416f-8e44-63d799418958 --source PARTLABEL=WDPurple6TB --mountpoint /media/ismail/WDPurple6TB --types ext4 --noheadings; then
        udisksctl unmount -b /dev/disk/by-label/WDPurple6TB
        udisksctl power-off -b /dev/disk/by-label/WDPurple6TB
        echo "Power-Off /dev/disk/by-label/WDPurple6TB"
    fi
}
export -f a b
parallel --lb ::: a b

或者：

umnt() {
    uuid="$1"
    label="$2"
    if findmnt --source UUID="$uuid" --source PARTLABEL="$label" --mountpoint /media/ismail/"$label" --types ext4 --noheadings; then
        udisksctl unmount -b /dev/disk/by-label/"$label"
        udisksctl power-off -b /dev/disk/by-label/"$label"
        echo "Power-Off /dev/disk/by-label/$label"
    fi
}
export -f umnt
parallel --lb umnt ::: 309689b5-ea5c-4175-84c7-192631553eab 151cf7f0-461a-416f-8e44-63d799418958 :::+ WDPurple8TB WDPurple6TB

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