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Date: Tue, 7 Oct 2025 12:38:37 +0100
Message-ID: <CANgSWMMdLZa=aN79XgJwYSHyX87bDzcmjEjWTeQL54aybS934A@mail.gmail.com>
Subject: job control in cygwin bash
To: cygwin AT cygwin DOT com
From: Vadym Krevs via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Vadym Krevs <vkrevs AT gmail DOT com>
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Sender: "Cygwin" <cygwin-bounces~archive-cygwin=delorie DOT com AT cygwin DOT com>

Hi.

I've a question regarding job control in cygwin bash.

Below is a simple program that prints out the process id of itself.

    C:\builds>cat a.c
    #include <stdio.h>
    #include <process.h>

    int main(int argc, char ** argv)
    {
            printf("pid=%d\n", _getpid());
            return 0;
    }

Compiling and running it in foreground from cygwin bash works as expected:

    user AT host /cygdrive/c/builds
    $ cl a.c
    Microsoft (R) C/C++ Optimizing Compiler Version 19.44.35217 for x86
    Copyright (C) Microsoft Corporation.  All rights reserved.

    a.c
    Microsoft (R) Incremental Linker Version 14.44.35217.0
    Copyright (C) Microsoft Corporation.  All rights reserved.

    /out:a.exe
    a.obj

    user AT host /cygdrive/c/builds
    $ ./a
    pid=2352


However, if I start it in background and attempt to get back the pid
of the started process via $!, the result is not what one would
expect. The actual process pid printed out from my program differs
from what cygwin bash thinks is "process ID of the job most recently
placed into the background".

    user AT host /cygdrive/c/builds
    $ ./a &
    [1] 15909

    user AT host /cygdrive/c/builds
    $ pid=27008
    echo $!
    15909
    [1]+  Done                    ./a


So my question is - is this a cygwin bash quirk (i.e. the fact that $!
is not the pid of the started process) caused by how fork/process
startup is implemented in cygwin? I have tried reading
https://cygwin.com/cygwin-ug-net/highlights.html#ov-hi-process but
could not see anything relevant aside from "Job control works as
expected in shells that support it." in the Signals section. Is there
any way to get the actual process pid?

Many thanks in advance,
Vadym

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