Bash:在while循环后保留变量的值 [英] Bash: Retain variable's value after while loop

问题描述

我的while循环结束后，我需要保留TEMP_FLAG的值.

I need to retain the value of TEMP_FLAG after my while loop ends.

#!/bin/bash

TEMP_FLAG=false

# loop over git log and set variable
git log --pretty="%H|%s" --skip=1 |
    while read commit; do 

        # do stuff like parsing the commit...

        # set variable     
        TEMP_FLAG=true 
    done

echo "$TEMP_FLAG" # <--- evaluates to false :(

我知道我的问题是由git log通过管道传递到while循环引起的，该循环产生了一个子shell，该子shell不会返回我的更新变量.

I know that my issue is caused by piping the git log to the while loop, which spawns a subshell that doesn't give back my updated variable.

但是，有一种方法可以在不更改管道的情况下实现我的预期行为吗?

However, is there a way get my intended behavior without changing the pipe?

推荐答案

使用管道时，您会自动创建子Shell，以便输入和输出可以被该Shell连接.这意味着您无法修改父环境，因为您现在处于子进程中.

When you use a pipe you are automatically creating subshells so that the input and output can be hooked up by the shell. That means that you cannot modify the parent environment, because you're now in a child process.

就像anubhava所说的那样，您可以像下面这样使用进程替换来重新构造循环以避免管道:

As anubhava said though, you can reformulate the loop to avoid the pipe by using process substitution like so:

while read commit; do
    TEMP_FLAG=true
done < <( git log --pretty="%H|%s" --skip=1 )

printf "%s\n" "$TEMP_FLAG"

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