并行运行if条件

Question

我的剧本是这样的：

#!/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，如果这两个if代码块并行运行会更好。但是，if代码块中的stdout & stderr应该是分组的(我的意思是它们的输出不应该重叠)。我的意思是：

以下三行的stdout和stderr应该在我们到达第一个if-fi代码块结束后显示。

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应该在我们到达第二个if代码块结束后显示。

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？

Answer 1

要序列化这些输出(和错误)，您必须临时保存其中的至少一个：

#! /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zsh的S =(...)进程替换形式创建临时文件。使用sh或bash，您可以使用系统上可用的mktemp或其他命令安全地创建临时文件。

严格地说，当zsh在展开的命令完成后立即删除临时文件时，=(cmd)并不意味着要这样使用。在这里，我们稍后使用相同的路径重新创建它，因此它并不是严格安全的，因为有一个小窗口，在这个窗口中，恶意参与者可以将文件重新创建为符号链接。

对于任何数量的并行卸载，我们可以分解一些东西。我们还可以向那些将要删除的诱惑文件打开fds，以便从一开始就删除它们，解决上面的问题并整理清理：

#! /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)

Answer 2

这是否有效：

#!/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