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Subject: Re: TMP/TEMP environment variable and /tmp
Date: Fri, 18 Sep 2020 07:56:47 +0200
Message-Id: <EA51058C-D017-4CCE-B207-C5EFD8CCC088@gmail.com>
References: <423c729e-4c66-dd5e-73c0-4c636089ea35 AT cornell DOT edu>
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To: Ken Brown <kbrown AT cornell DOT edu>
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From: Kristian Ivarsson via Cygwin <cygwin AT cygwin DOT com>
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>>>>>>>> Does anyone know the rational with this behaviour and what can be
>>>>>>>> done to get hold of the (real) Windows TMP/TEMP
>>>>>>>> environment-variable-values (in a
>>>>>>>> (hopefully) platform independent way) ?
>>>>>>> so if you are making your custom tree, try to stick on that
>>>>>>> expectation and have both directories.
>>>>>> In general, you are free to set TMP to a directory of your choice,
>>>>>> that's the purpose of that variable, no need to sync it with some root.
>>>>>> There is a comment in /etc/profile:
>>>>>>    # TMP and TEMP as defined in the Windows environment
>>>>>>    # can have unexpected consequences for cygwin apps, but it does not
>>>>>> explain what consequences that might be; probably some trouble with
>>>>>> ACL/access permissions for temporary files.
>>>>> Nowadays that would be $LOCALAPPDATA/Temp, or if you really insist, the
>>>>> content of /proc/registry/HKEY_CURRENT_USER/Environment/TMP (or TEMP),
>>>>> after similarly expanding environment variable references found in that.
>>>>> 
>>>>> The fact that getting Windows' idea of the user's TEMP directory is not
>>>>> immediately platform independent may well have been part of the rationale
>>>>> for not even trying that.
>>>> 
>>>> Well, at least it's up to the user
>>>> 
>>>> If the user sets its TMP-variable to "C:\Jabba Dabba Dooo" or "/jabba dabba doo", I expect the value of getenv("TMP") should be just that and regardless of OS the value returned is whatever the variable is set to and not magically changed to "/tmp"
>>> Of course and that's not happening, no worries. The issue was that TMP is set in /etc/profile and not inherited from the Windows environment.
>> Well, where my Cygwin-compiled-application is running, there’s no Cygwin-installation and thus no /etc/profile so it cannot be set there (if /etc/profile is not a built in resource in every executable), so there must be some text-value inside the compiled executables used in some manner somehow
> 
> There must be something going on in your environment that you haven't told us yet.  I just tried the following test case:
> 
> #include <stdio.h>
> #include <stdlib.h>
> int
> main ()
> {
>  printf ("The value of TMP is %s\n", getenv ("TMP"));
> }
> 
> In a Cygwin bash shell I get
> 
>  The value of TMP is /tmp
> 
> Running the same executable under a Windows Command Prompt, I get
> 
>  The value of TMP is /c/Users/kbrown/AppData/Local/Temp
> 
> So Cygwin converts TMP to a Posix path [*], but it doesn't change it to "/tmp".
> 
> Ken
> 
> [*] See environ.cc:303 for a list of environment variables that Cygwin converts.

Hmm, you’re right Ken

I tried this before taking off for a vacation and the Windows-TMP-variable is extracted

I now suspect that we maybe do have some logic that falls back to /tmp if the TMP-variable is NULL and perhaps the variable is NULL because we launch the process with CreateProcess and perhaps the environment-variables doesn’t get inherited then ?

The reason why we use CreateProcess from within a cygwin-application to create another cygwin-application (instead of fork or such) might seem weird, but it has its reasons

I need to confirm this after the vacation-trip or if someone already know if environment-variables “dissapear” if things such as CreateProcess are used ?

Best regards,
Kristian
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