Question

这是一个shell脚本。请将受控环境随机数生成子shell推断为在异步日志记录情况下使用它（我打算将它用于inotifywait输出）。

group=0
(
  for val in {1..10}; do 
    echo "$RANDOM/20000" | bc | xargs sleep # this waits 0, 1, or 2 seconds before each number is printed
    echo $val 
  done 
) | while true; do 
      while read -t 1 line; do 
        echo "read time=$group read=$line" 
      done
      ((group++))
    done

这会产生如下输出：

read time=1 read=1
read time=2 read=2
read time=2 read=3
read time=3 read=4
read time=3 read=5
read time=3 read=6
read time=4 read=7
read time=5 read=8
read time=5 read=9
read time=5 read=10

但它会挂起并且不会退出。它卡在外循环中，不断递增group：

$ echo $group 
1336794

显然，由于输入已完成，内循环已退出，变量的增量进入超级驱动。

如何退出循环？有没有类似else的某种类型的break子句，一旦输入完成后，我就可以破解内部for循环以便{{1}}退出外部循环？

当然，必须有一个更强大的方法，而不是在外循环中进行计时，看它是否过快。

Answer 1

#!/bin/bash
mkfifo outputs
for val in {1..10}; do
    echo "$RANDOM/20000" | bc | xargs sleep
    echo $val 
done > outputs &
group=0
time=$(date +%s%N)
while read line; do
    ctime=$(date +%s%N)
    [ $(( $ctime - $time )) -gt 1000000000 ] && let group++
    echo "read time=$group read=$line"
    time=$ctime
done < outputs

Answer 2

这是基于读取返回码的另一种解决方案。根据bash文档，当read -t退出超时时，它的返回码大于128，因此您可以区分EOF和超时。

function random_timed_output
{
  for val in {1..10}; do
    sleep $(( $RANDOM/20000 ))
    echo $val 
  done
}

group=0
random_timed_output | while true; do
  read -t 1 line
  rc=$?
  if [ $rc -gt 128 ]; then
    #read exit for timeout
    ((group++))
  elif [ $rc -gt 0 ]; then
    #read exit for error or EOF
    break
  else
    #read exit OK
    echo "read time=$group read=$line" 
  fi
done

Answer 3

 Kaizen ~/so_test $ cat zcntr.sh
 ilimit=10; ## the length of list in for loop ... 

grp=0
(   for val in {1..10}; do
     #echo "$RANDOM/10000" | bc | xargs sleep
     sleep $(($RANDOM/10000));
     echo $val
     done
 ) | while true; do

  while read -t 1 line; do
    echo "read time=$grp read=$line"
  done

  ((grp++));

  if [ $grp -eq $ilimit ]
     then
       break ;
  fi

done

输出效果不理想，但我稍后会看一下：

Kaizen ~/so_test $ ./zcntr.sh
  read time=0 read=1
  read time=0 read=2
  read time=1 read=
  read time=1 read=4
  read time=1 read=5
  ./zcntr.sh: line 13: read: read error: 0: Permission denied
  read time=4 read=7
  read time=6 read=
  read time=7 read=
  read time=7 read=10

无论如何都有帮助吗？

如果输入由内部“while read”处理，我怎么能打破shell脚本循环？

3 个答案: