-1

我有一个脚本

index=0
while read line 
do  
  echo "read line is $line" 
  line=`echo ${line}|awk '{print $1}'`  

  index=$((index+1)) 

  if((index%2==0));then 
    echo "before continue line is $line"  
    continue 
  fi   

  echo "index is $index and now modify html page with $line" 
  ...
  ...
  done< infile

infile 的内容是：

1OrMcP2CdV4 180 

1Wp33RG2XaA 180 

21zUUJ04ovI 180 

2pIqUhaDMLg 180 

2WRU4NUJSVc 180 
...
...

在infile中，有交替的空行，是我自己故意添加的，我为什么这样做，你可以参考http://goo.gl/K7g0m，这是“while read”循环的另一种奇怪行为。基本上，“读取”无法正确读取偶数行，因此我将偶数行设为空行。

我运行脚本，输出为：

read line is 1OrMcP2CdV4 180
index is 1 and now modify html page with 1OrMcP2CdV4


read line is 1Wp33RG2XaA 180
before continue line is 1Wp33RG2XaA


read line is 
index is 3 and now modify html page with 


read line is 21zUUJ04ovI 180
before continue line is 21zUUJ04ovI

read line is 
index is 5 and now modify html page with

所以基本上，“while read loop”似乎按顺序读取行：1 3 2 5 4

然后我修改了空行，比如

1OrMcP2CdV4 180 
Axxx
1Wp33RG2XaA 180 
Axxx
21zUUJ04ovI 180 
Axxx 
2pIqUhaDMLg 180 
Axxx  
2WRU4NUJSVc 180 
...
..

输出很有趣：

read line is 1OrMcP2CdV4 180
index is 1 and now modify html page with 1OrMcP2CdV4

read line is xxx
before continue line is xxx


read line is 1Wp33RG2XaA 180
index is 3 and now modify html page with 1Wp33RG2XaA

read line is xxx
before continue line is xxx

read line is 21zUUJ04ovI
index is 5 and now modify html page with 21zUUJ04ovI 


read line is 21zUUJ04ovI 180
before continue line is 21zUUJ04ovI

好的，它现在按顺序读取，但是偶数行“Axxx”被读取为“xxx”，前20行似乎是按顺序排列的，但有时，顺序又乱了！有趣又奇怪，不是吗？

这种行为不端有什么问题？对于脚本，有几个后台命令，比如

firefox &
tcpdump &

也喜欢

sleep 5

详情可以参考上面的链接，这样会不会有子进程同步的问题？但我不这么认为。

这个问题真的很奇怪，我真的不知道如何处理它！

4

1 回答 1

0

所以你想得到每第二行的第一个字段？然后我建议类似：

while read id rest 
do
     # here code to process id
     #  .....
     read again # skip every other line
done

顺便说一句：index你的代码中的初始值是多少？

于 2012-11-02T22:52:39.397 回答