变量值在子shell中丢失 [英] Variables value gets lost in subshell

问题描述

这个 bash 脚本将 jar 文件的名称连接到一个类路径(变量 CP)，在 while 循环中，该值是正确的，但在这个相关问题中描述的在子 shell 中丢失了 Bash 变量范围

This bash script concatenates the names for jar files to a classpath (variable CP), in the while loop the value is correct but is lost in the subshell as descibed in this related question Bash variable scope

#!/bin/bash
CP="AAA"
func() {
        ls -1 | while read JAR
        do
                if [ ! -z "$CP" ]; then
                        CP=${CP}':'
                fi
                CP=${CP}${JAR}
        done
        echo $CP # <-- prints AAA
}

func

我的问题是，由于我无法确定哪个元素将是最后一个，那么如何保存该值.

My question is, since I can't figure out which element will be the last one, how can the value be saved.

我真的需要将当前值(在循环中反复)保存到文件中吗?

Do I actually have to save the current value (repeatedly in the loop) to a file?

一位同事想出了这个运行良好的命令序列

A colleague came up with this command sequence which works well

ls | xargs echo|tr ' ' :

推荐答案

这里的问题是在管道中使用 while 会创建一个子 shell，而子 shell 不能影响其父级.您可以通过几种方式解决此问题.对于您现在正在做的事情，这就足够了:

The issue here is that using while in a pipeline creates a subshell, and a subshell cannot affect its parent. You can get around this in a few ways. For what you are doing now, this will suffice:

for JAR in *; do
    # Your stuff
done

另外要注意的是，你不应该依赖解析ls

Another thing to note is that you shouldn't rely on parsing ls

这还向您展示了避免使用子shell的方法.

This also shows you ways to avoid the subshell.

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