在bash不能使用变量出来，而与管 [英] Can't use a variable out of while and pipe in bash

问题描述

我有一个code一样，

  VAR =之前
回声$ someString| SED'$ someRegex|而读线
做
    如果[$条件];然后
        VAR =后
        回声$ VAR#first回声
    科幻
DONE
回声$ VAR#second回声
 

下面第一回声打印后，但第二个是之前。我怎样才能让第二回声打印之后。我认为这是因为管我买的不知道该怎么搞清楚。

感谢您的任何解决方案...

答案编辑：

我纠正它，它工作正常。尤金感谢您有用的答案

  VAR =之前
而读线
做
    如果[$条件];然后
        VAR =后
        回声$ VAR#first回声
    科幻
完成＆LT; ≤（回声$ someString| sed的'$ someRegex'）
回声$ VAR#second回声
 

解决方案

这样做的原因行为是一个，而循环中时，它的管道的一部分子shell运行。对于上面的，而循环，有自己的变量拷贝一个新的子shell VAR 创建

请参阅本文可能的解决方法：我设置的变量在一个循环，是在一个管道。为什么他们消失在循环终止后？或者说，为什么我不能管数据看？。

I have a code like that

var="before"  
echo "$someString" | sed '$someRegex' | while read line 
do
    if [ $condition ]; then
        var="after"
        echo "$var" #first echo
    fi 
done 
echo "$var" #second echo

Here first echo print "after", but second is "before". How can I make second echo print "after". I think it is because of pipe buy I don't know how figure out.

Thanks for any solutions...

answer edit:

I corrected it and it works fine. Thanks eugene for your useful answer

var="before"  
while read line 
do
    if [ $condition ]; then
        var="after"
        echo "$var" #first echo
    fi 
done < <(echo "$someString" | sed '$someRegex')
echo "$var" #second echo

解决方案

The reason for this behaviour is that a while loop runs in a subshell when it's part of a pipeline. For the while loop above, a new subshell with its own copy of the variable var is created.

See this article for possible workarounds: I set variables in a loop that's in a pipeline. Why do they disappear after the loop terminates? Or, why can't I pipe data to read?.

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