$$在子shell脚本VS $$ [英] $$ in a script vs $$ in a subshell

问题描述

$$给出脚本进程的进程ID在脚本中使用时，是这样的：

$$ gives process id of the script process when used in a script, like this:

例1

#!/bin/bash
# processid.sh
# print process ids

ps -o cmd,pid,ppid

echo "The value of \$\$ is $$"


$ ./processid.sh 
CMD                           PID  PPID
bash                        15073  4657
/bin/bash ./processid.sh    15326 15073
ps -o cmd,pid,ppid          15327 15326
The value of $$ is 15326

请遵守$$给出的PID和PS是的 15326

我的shell提示符是PID的 15073

My shell prompt is pid 15073

但在子shell，$$给父shell（即15073）

But in a subshell, $$ gives pid of parent shell ( which is 15073)

例2

$ ( ps -o cmd,pid,ppid ; echo $$ )
CMD                           PID  PPID
bash                        15073  4657
bash                        15340 15073
ps -o cmd,pid,ppid          15341 15340
15073

下面子shell为PID 15340

Here subshell is pid 15340

问：为什么呢？是不是剧本也处于子shell运行？例如什么2子shell和外壳在该脚本示例1中运行之间的区别？

Question: Why so ? Isn't the script also running in a subshell ? Whats the difference between the subshell in example 2 and the shell in which the script runs in example 1 ?

推荐答案

我试过和逃避（传递给$$子shell）作为子shell继承父猛砸$$值不起作用。解决这个问题的解决方法是使用$ BASHPID。

I tried and escaping (to pass the $$ to the subshell) does not work as the subshell inherits the $$ value from the parent bash. The solution to this is to use $BASHPID.

(echo $$; echo $BASHPID)

从父shell和子shell打印PID。

prints the PID from the parent shell and from the subshell.

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