[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: $PPID behave differently in 5.1 and 4.3

From: Eduardo Bustamante
Subject: Re: $PPID behave differently in 5.1 and 4.3
Date: Sun, 16 May 2021 10:17:46 -0700

On Sun, May 16, 2021 at 1:38 AM leodream <leodream2008@gmail.com> wrote:
> I created 2 scripts like below
> <http://gnu-bash.2382.n7.nabble.com/file/t3303/Screenshot_20210516_163002.png>
> Running the test1.sh with bash 5.1 will have different PPID printed by the
> last test2.sh call when it is executed in sub-shell.
> For bash 4.3, the script will output consistent PPID.
> <http://gnu-bash.2382.n7.nabble.com/file/t3303/Screenshot_20210516_163523.png>
> It looks like something had been changed regarding the sub-shell execution
> in later Bash versions?

Yes. See the following entries in the 5.1 changelog

$ grep optimize CHANGES-5.1
c. Bash attempts to optimize away forks in the last command in a function body
b. Bash attempts to optimize the number of times it forks when executing

What you're seeing is that bash notices that it can optimize the
function call by avoiding a fork when calling "test2.sh" the third
time, thus the parent PID is different. This is done by the
`optimize_shell_function` in builtins/evalstring.c.

By the way, in the future, avoid sending scripts as screenshots and
instead just send them as plain text.  It makes it more difficult for
us to help you because now we have to transcribe your code from a
picture and hope that we didn't make any mistakes along the way.

reply via email to

[Prev in Thread] Current Thread [Next in Thread]